diff --git a/README.md b/README.md
index 0262c56..702e90c 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,6 @@
-# upload-generator
+# upload-generator (ARCHIVE)
+
+> This project has been superseded by my current web gallery build system. It won't receive any more updates.
 
 Script to generate multi-gallery upload-ready files.
 
@@ -7,9 +9,32 @@ Script to generate multi-gallery upload-ready files.
 - A Python environment to install dependencies (`pip install -r requirements.txt`); if unsure, create a fresh one with `virtualenv venv`.
 - LibreOffice 6.0+, making sure that `libreoffice` is in your PATH.
 
+## Installation
+
+I recommend creating a virtualenv first. Linux/macOS/Unix example:
+
+```sh
+virtualenv venv
+source venv/bin/activate  # Also run every time you use this tool
+pip install -r requirements.txt
+activate-global-python-argcomplete
+```
+
+Windows example (autocompletion is not available):
+
+```powershell
+virtualenv venv
+.\venv\Scripts\activate  # Also run every time you use this tool
+pip install -r requirements.txt
+```
+
+## Testing
+
+Run `python test.py`.
+
 ## Usage
 
-Run with `python main.py -h` for options. Generated files are output to `./out` by default.
+Run with `python main.py -h` (or simply `./main.py -h`) for options. Generated files are output to `./out` by default.
 
 ### Story files
 
@@ -29,43 +54,69 @@ In order to parse descriptions, you need a configuration file (default path is `
 }
 ```
 
-Uppercase letters are optional. Only include your username for websites that you wish to generate descriptions for.
+Uppercase letters for usernames are optional. Only include your username for websites that you wish to generate descriptions/stories for.
+
+#### Basic formatting
 
 Input descriptions should be formatted as BBCode. The following tags are accepted:
 
 ```bbcode
 [b]Bold text[/b]
 [i]Italic text[/i]
-[url=https://github.com]URL link[/url]
+[u]Underline text[/u]
+[center]Center-aligned text[/center]
+[url=https://github.com/BadMannersXYZ]URL link[/url]
 ```
 
-There are also special tags to link to yourself or other users automatically. This may include websites not available in the configuration:
+#### Self-link formatting
+
+`[self][/self]` will create a link to yourself for each website, with the same formatting as the `[user]...[/user]` switch. The inside of this tag must be always empty.
+
+#### Conditional formatting
+
+Another special set of tags is `[if=...][/if]` or `[if=...][/if][else][/else]`. The `if` tag lets you conditionally show content . The `else` tag is optional but must appear immediately after an `if` tag (no whitespace in-between), and displays whenever the condition is false instead.
+
+The following parameters are available:
+
+- `site`: generated according to the target website, eg. `[if=site==fa]...[/if]` or `[if=site!=furaffinity]...[/if][else]...[/else]`
+- `define`: generated according to argument(s) defined to the script into the command line (i.e. with the `-D / --define-option` flag), eg. `[if=define==prod]...[/if][else]...[/else]` or `[if=define in possible_flag_1,possible_flag_2]...[/if][else]...[/else]`
+
+The following conditions are available:
+
+- `==`: eg. `[if=site==eka]Only show this on Eka's Portal.[/if][else]Show this everywhere except Eka's Portal![/else]`
+- `!=`: eg. `[if=site!=eka]Show this everywhere except Eka's Portal![/if]`
+- ` in `: eg. `[if=site in eka,fa]Only show this on Eka's Portal or Fur Affinity...[/if]`
+
+#### Switch formatting
+
+You can use special switch tags, which will generate different information per website automatically. There are two options available: creating different URLs per website, or linking to different users.
 
 ```bbcode
-[self][/self]
+Available for both [user]...[/user] and [siteurl]...[/siteurl] tags
+- [generic=https://example.com/GenericUser]Generic text to display[/generic]
+- [eka=EkasPortalUser][/eka] [aryion=EkasPortalUser][/aryion]
+- [fa=FurAffinityUser][/fa] [furaffinity=FurAffinityUser][/furaffinity]
+- [weasyl=WeasylUser][/weasyl]
+- [ib=InkbunnyUser][/ib] [inkbunnny=InkbunnyUser][/inkbunnny]
+- [sf=SoFurryUser][/sf] [sofurry=SoFurryUser][/sofurry]
 
-[eka]EkasPortalUser[/eka]
-[fa]FurAffinityUser[/fa]
-[weasyl]WeasylUser[/weasyl]
-[ib]InkbunnyUser[/ib]
-[sf]SoFurryUser[/sf]
-[twitter]@TwitterUser[/twitter] - Leading '@' is optional
-[mastodon]@MastodonUser@mastodoninstance.com[/mastodon] - Leading '@' is optional
+Available only for [user]...[/user]
+- [twitter=@TwitterUser][/twitter] - Leading '@' is optional
+- [mastodon=@MastodonUser@mastodoninstance.com][/mastodon] - Leading '@' is optional
 ```
 
-`[self][/self]` tags must always be empty. The other tags are nestable and flexible, allowing attributes to display information differently on each supported website. Some examples:
+These tags are nestable and flexible, requiring attributes to display information differently on each supported website. Some examples:
 
 ```bbcode
-[eka=Lorem][/eka] is equivalent to [eka]Lorem[/eka].
+[user][eka]Lorem[/eka][/user] is equivalent to [user][eka=Lorem][/eka][/user].
 
-[fa=Ipsum]Dolor[/fa] shows Ipsum's username on FurAffinity, and Dolor everywhere else as a link to Ipsum's FA userpage.
+[user][fa=Ipsum]Dolor[/fa][/user] shows Ipsum's username on Fur Affinity, and "Dolor" everywhere else with a link to Ipsum's userpage on FA.
 
-[weasyl=Sit][ib=Amet][/ib][/weasyl] will show the two user links on Weasyl and Inkbunny as expected. For other websites, the innermost tag is prioritized - Inkbunny, in this case.
-[ib=Amet][weasyl=Sit][/weasyl][/ib] is the same as above, but the Weasyl link is prioritized instead.
+[user][ib=Sit][weasyl=Amet][twitter=Consectetur][/twitter][/weasyl][/ib][/user] will show a different usernames on Inkbunny and Weasyl. For other websites, the innermost user name and link are prioritized - Twitter, in this case.
+[user][ib=Sit][twitter=Consectetur][weasyl=Amet][/weasyl][/twitter][/ib][/user] is similar, but the Weasyl user data is prioritized for websites other than Inkbunny. In this case, the Twitter tag is rendered useless, since descriptions can't be generated for the website.
 
-[ib=Amet][weasyl=Sit]Consectetur[/weasyl][/ib] is the same as above, but Consectetur is displayed as the username for websites other than Inkbunny and Weasyl, with a link to the Weasyl gallery.
+[siteurl][sf=https://a.com][eka=https://b.com]Adipiscing[/eka][/sf][/siteurl] displays links on SoFurry and Eka's Portal, with "Adipiscing" as the link's text. Other websites won't display any link.
+[siteurl][sf=https://a.com][eka=https://b.com][generic=https://c.com]Adipiscing[/generic][/eka][/sf][/siteurl] is the same as above, but with the innermost generic tag serving as a fallback, guaranteeing that a link will be generated for all websites.
 
-[generic=https://github.com/BadMannersXYZ]Bad Manners[/generic] can be used as the innermost tag with a mandatory URL attribute and default username, and is similar to the URL tag, but it can be nested within other profile links. Those other profile links get used only at their respective websites.
+[user][fa=Elit][generic=https://github.com/BadMannersXYZ]Bad Manners[/generic][/fa][/user] shows how a generic tag can be used for user links as well, displayed everywhere aside from Fur Affinity in this example. User tags don't need an explicit fallback - the innermost tag is always used as a fallback for user links.
 ```
-
-Another special set of tags is `[if][/if]` and `[else][/else]`. The if tag receives a parameter for the condition (i.e. `[if=parameter==value]...[/if]` or `[if=parameter!=value]...[/if]`) to check on the current transformer, and lets you show or omit generated content respectively. The else tag is optional but must appear immediately after an if tag (no whitespace in-between), and displays whenever the condition is false instead. For now, the if tag only accepts the `site` parameter (eg. `[if=site==fa]...[/if][else]...[/else]` or `[if=site!=furaffinity]...[/if]`).
diff --git a/description.py b/description.py
index cfb8090..bcdb4cd 100644
--- a/description.py
+++ b/description.py
@@ -3,12 +3,18 @@ import io
 import json
 import lark
 import os
+import psutil
 import re
 import subprocess
 import typing
 
+from sites import SUPPORTED_SITE_TAGS
 
-SUPPORTED_USER_TAGS = ['eka', 'fa', 'weasyl', 'ib', 'sf', 'twitter', 'mastodon']
+SUPPORTED_USER_TAGS: typing.Mapping[str, typing.Set[str]] = {
+  **SUPPORTED_SITE_TAGS,
+  'twitter': {'twitter'},
+  'mastodon': {'mastodon'},
+}
 
 DESCRIPTION_GRAMMAR = r"""
   ?start: document_list
@@ -18,39 +24,58 @@ DESCRIPTION_GRAMMAR = r"""
   document: b_tag
           | i_tag
           | u_tag
+          | center_tag
           | url_tag
           | self_tag
           | if_tag
           | user_tag_root
+          | siteurl_tag_root
           | TEXT
 
   b_tag: "[b]" [document_list] "[/b]"
   i_tag: "[i]" [document_list] "[/i]"
   u_tag: "[u]" [document_list] "[/u]"
+  center_tag: "[center]" [document_list] "[/center]"
   url_tag: "[url" ["=" [URL]] "]" [document_list] "[/url]"
 
   self_tag: "[self][/self]"
-  if_tag: "[if=" CONDITION "]" [document_list] "[/if]" [ "[else]" document_list "[/else]" ]
+  if_tag: "[if=" CONDITION "]" [document_list] "[/if]" [ "[else]" [document_list] "[/else]" ]
 
-  user_tag_root: user_tag
-  user_tag: generic_tag | """
+  user_tag_root: "[user]" user_tag "[/user]"
+  user_tag: user_tag_generic | """
 
-DESCRIPTION_GRAMMAR += ' | '.join(f'{tag}_tag' for tag in SUPPORTED_USER_TAGS)
-DESCRIPTION_GRAMMAR += ''.join(f'\n  {tag}_tag: "[{tag}" ["=" USERNAME] "]" USERNAME "[/{tag}]" | "[{tag}" "=" USERNAME  "]" [user_tag] "[/{tag}]"' for tag in SUPPORTED_USER_TAGS)
+DESCRIPTION_GRAMMAR += ' | '.join(f'user_tag_{tag}' for tag in SUPPORTED_USER_TAGS)
+for tag, alts in SUPPORTED_USER_TAGS.items():
+  DESCRIPTION_GRAMMAR += f'\n  user_tag_{tag}: '
+  DESCRIPTION_GRAMMAR += ' | '.join(f'"[{alt}" ["=" USERNAME] "]" USERNAME "[/{alt}]" | "[{alt}" "=" USERNAME  "]" [user_tag] "[/{alt}]"' for alt in alts)
 
 DESCRIPTION_GRAMMAR += r"""
-  generic_tag: "[generic=" URL "]" USERNAME "[/generic]"
+  user_tag_generic: "[generic=" URL "]" USERNAME "[/generic]"
 
-  USERNAME: /[a-zA-Z0-9][a-zA-Z0-9 _-]*/
-  URL: /(https?:\/\/)?[^\]]+/
+  siteurl_tag_root: "[siteurl]" siteurl_tag "[/siteurl]"
+  siteurl_tag: siteurl_tag_generic | """
+
+DESCRIPTION_GRAMMAR += ' | '.join(f'siteurl_tag_{tag}' for tag in SUPPORTED_SITE_TAGS)
+for tag, alts in SUPPORTED_SITE_TAGS.items():
+  DESCRIPTION_GRAMMAR += f'\n  siteurl_tag_{tag}: '
+  DESCRIPTION_GRAMMAR += ' | '.join(f'"[{alt}" "=" URL "]" ( siteurl_tag | TEXT ) "[/{alt}]"' for alt in alts)
+
+DESCRIPTION_GRAMMAR += r"""
+  siteurl_tag_generic: "[generic=" URL "]" TEXT "[/generic]"
+
+  USERNAME: / *@?[a-zA-Z0-9][a-zA-Z0-9 @._-]*/
+  URL: / *(https?:\/\/)?[^\]]+ */
   TEXT: /([^\[]|[ \t\r\n])+/
-  CONDITION: / *[a-z]+ *(==|!=) *[a-zA-Z0-9]+ */
+  CONDITION: / *[a-z]+ *(==|!=) *[a-zA-Z0-9_-]+ *| *[a-z]+ +in +([a-zA-Z0-9_-]+ *, *)*[a-zA-Z0-9_-]+ */
 """
 
 DESCRIPTION_PARSER = lark.Lark(DESCRIPTION_GRAMMAR, parser='lalr')
 
 
-class UserTag:
+class DescriptionParsingError(ValueError):
+  pass
+
+class SiteSwitchTag:
   def __init__(self, default: typing.Optional[str]=None, **kwargs):
     self.default = default
     self._sites: typing.OrderedDict[str, typing.Optional[str]] = OrderedDict()
@@ -70,30 +95,53 @@ class UserTag:
   def __getitem__(self, name: str) -> typing.Optional[str]:
     return self._sites.get(name)
 
+  def __contains__(self, name: str) -> bool:
+    return name in self._sites
+
   @property
   def sites(self):
     yield from self._sites
 
 class UploadTransformer(lark.Transformer):
-  def __init__(self, *args, **kwargs):
-    super(UploadTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, define_options=set(), *args, **kwargs):
+    super().__init__(*args, **kwargs)
+    self.define_options = define_options
+    # Init user_tag_xxxx methods
     def _user_tag_factory(tag):
-      # Create a new UserTag if innermost node, or append to list in order
+      # Create a new user SiteSwitchTag if innermost node, or append to list in order
       def user_tag(data):
         attribute, inner = data[0], data[1]
         if attribute and attribute.strip():
-          if isinstance(inner, UserTag):
+          if isinstance(inner, SiteSwitchTag):
             inner[tag] = attribute.strip()
             return inner
-          user = UserTag(default=inner and inner.strip())
+          user = SiteSwitchTag(default=inner and inner.strip())
           user[tag] = attribute.strip()
           return user
-        user = UserTag()
+        user = SiteSwitchTag()
         user[tag] = inner.strip()
         return user
       return user_tag
     for tag in SUPPORTED_USER_TAGS:
-      setattr(self, f'{tag}_tag', _user_tag_factory(tag))
+      setattr(self, f'user_tag_{tag}', _user_tag_factory(tag))
+    # Init siteurl_tag_xxxx methods
+    def _siteurl_tag_factory(tag):
+      # Create a new siteurl SiteSwitchTag if innermost node, or append to list in order
+      def siteurl_tag(data):
+        attribute, inner = data[0], data[1]
+        if attribute and attribute.strip():
+          if isinstance(inner, SiteSwitchTag):
+            inner[tag] = attribute.strip()
+            return inner
+          siteurl = SiteSwitchTag(default=inner and inner.strip())
+          siteurl[tag] = attribute.strip()
+          return siteurl
+        siteurl = SiteSwitchTag()
+        siteurl[tag] = inner.strip()
+        return siteurl
+      return siteurl_tag
+    for tag in SUPPORTED_SITE_TAGS:
+      setattr(self, f'siteurl_tag_{tag}', _siteurl_tag_factory(tag))
 
   def document_list(self, data):
     return ''.join(data)
@@ -110,6 +158,9 @@ class UploadTransformer(lark.Transformer):
   def u_tag(self, _):
     raise NotImplementedError('UploadTransformer.u_tag is abstract')
 
+  def center_tag(self, _):
+    raise NotImplementedError('UploadTransformer.center_tag is abstract')
+
   def url_tag(self, _):
     raise NotImplementedError('UploadTransformer.url_tag is abstract')
 
@@ -119,57 +170,86 @@ class UploadTransformer(lark.Transformer):
   def transformer_matches_site(self, site: str) -> bool:
     raise NotImplementedError('UploadTransformer.transformer_matches_site is abstract')
 
+  def transformer_matches_define(self, option: str) -> bool:
+    return option in self.define_options
+
   def if_tag(self, data: typing.Tuple[str, str, str]):
-    condition, truthy_document, falsy_document = data
-    equality_condition = condition.split('==')
+    condition, truthy_document, falsy_document = data[0], data[1], data[2]
+    # Test equality condition, i.e. `site==foo`
+    equality_condition = condition.split('==', 1)
     if len(equality_condition) == 2 and equality_condition[1].strip():
       conditional_test = f'transformer_matches_{equality_condition[0].strip()}'
       if hasattr(self, conditional_test):
         if getattr(self, conditional_test)(equality_condition[1].strip()):
           return truthy_document or ''
         return falsy_document or ''
-    inequality_condition = condition.split('!=')
+    # Test inequality condition, i.e. `site!=foo`
+    inequality_condition = condition.split('!=', 1)
     if len(inequality_condition) == 2 and inequality_condition[1].strip():
       conditional_test = f'transformer_matches_{inequality_condition[0].strip()}'
       if hasattr(self, conditional_test):
         if not getattr(self, conditional_test)(inequality_condition[1].strip()):
           return truthy_document or ''
         return falsy_document or ''
+    # Test inclusion condition, i.e. `site in foo,bar`
+    inclusion_condition = condition.split(' in ', 1)
+    if len(inclusion_condition) == 2 and inclusion_condition[1].strip():
+      conditional_test = f'transformer_matches_{inclusion_condition[0].strip()}'
+      if hasattr(self, conditional_test):
+        matches = (parameter.strip() for parameter in inclusion_condition[1].split(','))
+        if any(getattr(self, conditional_test)(match) for match in matches):
+          return truthy_document or ''
+        return falsy_document or ''
     raise ValueError(f'Invalid [if][/if] tag condition: {condition}')
 
   def user_tag_root(self, data):
-    user_data: UserTag = data[0]
+    user_data: SiteSwitchTag = data[0]
     for site in user_data.sites:
       if site == 'generic':
-        return self.url_tag((user_data['generic'].strip(), user_data.default))
-      elif site == 'eka':
-        return self.url_tag((f'https://aryion.com/g4/user/{user_data["eka"]}', user_data.default or user_data["eka"]))
-      elif site == 'fa':
-        return self.url_tag((f'https://furaffinity.net/user/{user_data["fa"].replace("_", "")}', user_data.default or user_data['fa']))
+        return self.url_tag((user_data['generic'], user_data.default))
+      elif site == 'aryion':
+        return self.url_tag((f'https://aryion.com/g4/user/{user_data["aryion"]}', user_data.default or user_data["aryion"]))
+      elif site == 'furaffinity':
+        return self.url_tag((f'https://furaffinity.net/user/{user_data["furaffinity"].replace("_", "")}', user_data.default or user_data['furaffinity']))
       elif site == 'weasyl':
         return self.url_tag((f'https://www.weasyl.com/~{user_data["weasyl"].replace(" ", "").lower()}', user_data.default or user_data['weasyl']))
-      elif site == 'ib':
-        return self.url_tag((f'https://inkbunny.net/{user_data["ib"]}', user_data.default or user_data['ib']))
-      elif site == 'sf':
-        return self.url_tag((f'https://{user_data["sf"].replace(" ", "-").lower()}.sofurry.com', user_data.default or user_data['sf']))
+      elif site == 'inkbunny':
+        return self.url_tag((f'https://inkbunny.net/{user_data["inkbunny"]}', user_data.default or user_data['inkbunny']))
+      elif site == 'sofurry':
+        return self.url_tag((f'https://{user_data["sofurry"].replace(" ", "-").lower()}.sofurry.com', user_data.default or user_data['sofurry']))
       elif site == 'twitter':
         return self.url_tag((f'https://twitter.com/{user_data["twitter"].rsplit("@", 1)[-1]}', user_data.default or user_data['twitter']))
       elif site == 'mastodon':
         *_, mastodon_user, mastodon_instance = user_data["mastodon"].rsplit('@', 2)
-        return self.url_tag((f'https://{mastodon_instance}/@{mastodon_user}', user_data.default or user_data['mastodon']))
+        return self.url_tag((f'https://{mastodon_instance.strip()}/@{mastodon_user.strip()}', user_data.default or user_data['mastodon']))
       else:
         print(f'Unknown site "{site}" found in user tag; ignoring...')
-    raise TypeError('Invalid UserTag data')
+    raise TypeError('Invalid user SiteSwitchTag data - no matches found')
 
   def user_tag(self, data):
     return data[0]
 
-  def generic_tag(self, data):
+  def user_tag_generic(self, data):
     attribute, inner = data[0], data[1]
-    user = UserTag(default=inner.strip())
+    user = SiteSwitchTag(default=inner.strip())
     user['generic'] = attribute.strip()
     return user
 
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'generic' in siteurl_data:
+      return self.url_tag((siteurl_data['generic'], siteurl_data.default))
+    return ''
+
+  def siteurl_tag(self, data):
+    return data[0]
+
+  def siteurl_tag_generic(self, data):
+    attribute, inner = data[0], data[1]
+    siteurl = SiteSwitchTag(default=inner.strip())
+    siteurl['generic'] = attribute.strip()
+    return siteurl
+
 class BbcodeTransformer(UploadTransformer):
   def b_tag(self, data):
     if data[0] is None or not data[0].strip():
@@ -186,8 +266,15 @@ class BbcodeTransformer(UploadTransformer):
       return ''
     return f'[u]{data[0]}[/u]'
 
+  def center_tag(self, data):
+    if data[0] is None or not data[0].strip():
+      return ''
+    return f'[center]{data[0]}[/center]'
+
   def url_tag(self, data):
-    return f'[url={data[0] or ""}]{data[1] or ""}[/url]'
+    if data[0] is None or not data[0].strip():
+      return data[1].strip() if data[1] else ''
+    return f'[url={data[0].strip()}]{data[1] if data[1] and data[1].strip() else data[0].strip()}[/url]'
 
 class MarkdownTransformer(UploadTransformer):
   def b_tag(self, data):
@@ -206,7 +293,9 @@ class MarkdownTransformer(UploadTransformer):
     return f'<u>{data[0]}</u>'  # Markdown should support simple HTML tags
 
   def url_tag(self, data):
-    return f'[{data[1] or ""}]({data[0] or ""})'
+    if data[0] is None or not data[0].strip():
+      return data[1].strip() if data[1] else ''
+    return f'[{data[1] if data[1] and data[1].strip() else data[0].strip()}]({data[0].strip()})'
 
 class PlaintextTransformer(UploadTransformer):
   def b_tag(self, data):
@@ -218,141 +307,210 @@ class PlaintextTransformer(UploadTransformer):
   def u_tag(self, data):
     return str(data[0]) if data[0] else ''
 
+  def center_tag(self, data):
+    return str(data[0]) if data[0] else ''
+
   def url_tag(self, data):
+    if data[0] is None or not data[0].strip():
+      return data[1] if data[1] and data[1].strip() else ''
     if data[1] is None or not data[1].strip():
-      return str(data[0]) if data[0] else ''
-    return f'{data[1].strip()}: {data[0] or ""}'
+      return data[0].strip()
+    return f'{data[1]}: {data[0].strip()}'
 
   def user_tag_root(self, data):
     user_data = data[0]
     for site in user_data.sites:
       if site == 'generic':
         break
-      elif site == 'eka':
-        return f'{user_data["eka"]} on Eka\'s Portal'
-      elif site == 'fa':
-        return f'{user_data["fa"]} on Fur Affinity'
+      elif site == 'aryion':
+        return f'{user_data["aryion"]} on Eka\'s Portal'
+      elif site == 'furaffinity':
+        return f'{user_data["furaffinity"]} on Fur Affinity'
       elif site == 'weasyl':
         return f'{user_data["weasyl"]} on Weasyl'
-      elif site == 'ib':
-        return f'{user_data["ib"]} on Inkbunny'
-      elif site == 'sf':
-        return f'{user_data["sf"]} on SoFurry'
+      elif site == 'inkbunny':
+        return f'{user_data["inkbunny"]} on Inkbunny'
+      elif site == 'sofurry':
+        return f'{user_data["sofurry"]} on SoFurry'
       elif site == 'twitter':
         return f'@{user_data["twitter"].rsplit("@", 1)[-1]} on Twitter'
       elif site == 'mastodon':
         *_, mastodon_user, mastodon_instance = user_data["mastodon"].rsplit('@', 2)
-        return f'@{mastodon_user} on {mastodon_instance}'
+        return f'@{mastodon_user.strip()} on {mastodon_instance.strip()}'
       else:
         print(f'Unknown site "{site}" found in user tag; ignoring...')
-    return super(PlaintextTransformer, self).user_tag_root(data)
+    return super().user_tag_root(data)
 
 class AryionTransformer(BbcodeTransformer):
-  def __init__(self, self_user, *args, **kwargs):
-    super(AryionTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, self_user=None, *args, **kwargs):
+    super().__init__(*args, **kwargs)
     def self_tag(data):
-      return self.user_tag_root((UserTag(eka=self_user),))
+      if self_user:
+        return self.user_tag_root((SiteSwitchTag(aryion=self_user),))
+      raise ValueError('self_tag is unavailable for AryionTransformer - no user provided')
     self.self_tag = self_tag
 
-  def transformer_matches_site(self, site: str) -> bool:
-    return site in ('eka', 'aryion')
+  @staticmethod
+  def transformer_matches_site(site: str) -> bool:
+    return site in SUPPORTED_USER_TAGS['aryion']
 
   def user_tag_root(self, data):
-    user_data = data[0]
-    if user_data['eka']:
-      return f':icon{user_data["eka"]}:'
-    return super(AryionTransformer, self).user_tag_root(data)
+    user_data: SiteSwitchTag = data[0]
+    if user_data['aryion']:
+      return f':icon{user_data["aryion"]}:'
+    return super().user_tag_root(data)
+
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'aryion' in siteurl_data:
+      return self.url_tag((siteurl_data['aryion'], siteurl_data.default))
+    return super().siteurl_tag_root(data)
 
 class FuraffinityTransformer(BbcodeTransformer):
-  def __init__(self, self_user, *args, **kwargs):
-    super(FuraffinityTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, self_user=None, *args, **kwargs):
+    super().__init__(*args, **kwargs)
     def self_tag(data):
-      return self.user_tag_root((UserTag(fa=self_user),))
+      if self_user:
+        return self.user_tag_root((SiteSwitchTag(furaffinity=self_user),))
+      raise ValueError('self_tag is unavailable for FuraffinityTransformer - no user provided')
     self.self_tag = self_tag
 
-  def transformer_matches_site(self, site: str) -> bool:
-    return site in ('fa', 'furaffinity')
+  @staticmethod
+  def transformer_matches_site(site: str) -> bool:
+    return site in SUPPORTED_USER_TAGS['furaffinity']
 
   def user_tag_root(self, data):
-    user_data = data[0]
-    if user_data['fa']:
-      return f':icon{user_data["fa"]}:'
-    return super(FuraffinityTransformer, self).user_tag_root(data)
+    user_data: SiteSwitchTag = data[0]
+    if user_data['furaffinity']:
+      return f':icon{user_data["furaffinity"]}:'
+    return super().user_tag_root(data)
+
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'furaffinity' in siteurl_data:
+      return self.url_tag((siteurl_data['furaffinity'], siteurl_data.default))
+    return super().siteurl_tag_root(data)
 
 class WeasylTransformer(MarkdownTransformer):
-  def __init__(self, self_user, *args, **kwargs):
-    super(WeasylTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, self_user=None, *args, **kwargs):
+    super().__init__(*args, **kwargs)
     def self_tag(data):
-      return self.user_tag_root((UserTag(weasyl=self_user),))
+      if self_user:
+        return self.user_tag_root((SiteSwitchTag(weasyl=self_user),))
+      raise ValueError('self_tag is unavailable for WeasylTransformer - no user provided')
     self.self_tag = self_tag
 
-  def transformer_matches_site(self, site: str) -> bool:
+  @staticmethod
+  def transformer_matches_site(site: str) -> bool:
     return site == 'weasyl'
 
+  def center_tag(self, data):
+    if data[0] is None or not data[0].strip():
+      return ''
+    return f'<div class="align-center">{data[0]}</div>'
+
   def user_tag_root(self, data):
-    user_data = data[0]
+    user_data: SiteSwitchTag = data[0]
     if user_data['weasyl']:
       return f'<!~{user_data["weasyl"].replace(" ", "")}>'
-    if user_data.default is None:
-      for site in user_data.sites:
-        if site == 'fa':
-          return f'<fa:{user_data["fa"]}>'
-        if site == 'ib':
-          return f'<ib:{user_data["ib"]}>'
-        if site == 'sf':
-          return f'<sf:{user_data["sf"]}>'
-    return super(WeasylTransformer, self).user_tag_root(data)
+    for site in user_data.sites:
+      if site == 'furaffinity':
+        return f'<fa:{user_data["furaffinity"]}>'
+      if site == 'inkbunny':
+        return f'<ib:{user_data["inkbunny"]}>'
+      if site == 'sofurry':
+        return f'<sf:{user_data["sofurry"]}>'
+    return super().user_tag_root(data)
+
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'weasyl' in siteurl_data:
+      return self.url_tag((siteurl_data['weasyl'], siteurl_data.default))
+    return super().siteurl_tag_root(data)
 
 class InkbunnyTransformer(BbcodeTransformer):
-  def __init__(self, self_user, *args, **kwargs):
-    super(InkbunnyTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, self_user=None, *args, **kwargs):
+    super().__init__(*args, **kwargs)
     def self_tag(data):
-      return self.user_tag_root((UserTag(ib=self_user),))
+      if self_user:
+        return self.user_tag_root((SiteSwitchTag(inkbunny=self_user),))
+      raise ValueError('self_tag is unavailable for InkbunnyTransformer - no user provided')
     self.self_tag = self_tag
 
-  def transformer_matches_site(self, site: str) -> bool:
-    return site in ('ib', 'inkbunny')
+  @staticmethod
+  def transformer_matches_site(site: str) -> bool:
+    return site in SUPPORTED_USER_TAGS['inkbunny']
 
   def user_tag_root(self, data):
-    user_data = data[0]
-    if user_data['ib']:
-      return f'[iconname]{user_data["ib"]}[/iconname]'
-    if user_data.default is None:
-      for site in user_data.sites:
-        if site == 'fa':
-          return f'[fa]{user_data["fa"]}[/fa]'
-        if site == 'sf':
-          return f'[sf]{user_data["sf"]}[/sf]'
-        if site == 'weasyl':
-          return f'[weasyl]{user_data["weasyl"].replace(" ", "").lower()}[/weasyl]'
-    return super(InkbunnyTransformer, self).user_tag_root(data)
+    user_data: SiteSwitchTag = data[0]
+    if user_data['inkbunny']:
+      return f'[iconname]{user_data["inkbunny"]}[/iconname]'
+    for site in user_data.sites:
+      if site == 'furaffinity':
+        return f'[fa]{user_data["furaffinity"]}[/fa]'
+      if site == 'sofurry':
+        return f'[sf]{user_data["sofurry"]}[/sf]'
+      if site == 'weasyl':
+        return f'[weasyl]{user_data["weasyl"].replace(" ", "").lower()}[/weasyl]'
+    return super().user_tag_root(data)
+
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'inkbunny' in siteurl_data:
+      return self.url_tag((siteurl_data['inkbunny'], siteurl_data.default))
+    return super().siteurl_tag_root(data)
 
 class SoFurryTransformer(BbcodeTransformer):
-  def __init__(self, self_user, *args, **kwargs):
-    super(SoFurryTransformer, self).__init__(*args, **kwargs)
+  def __init__(self, self_user=None, *args, **kwargs):
+    super().__init__(*args, **kwargs)
     def self_tag(data):
-      return self.user_tag_root((UserTag(sf=self_user),))
+      if self_user:
+        return self.user_tag_root((SiteSwitchTag(sofurry=self_user),))
+      raise ValueError('self_tag is unavailable for SoFurryTransformer - no user provided')
     self.self_tag = self_tag
 
-  def transformer_matches_site(self, site: str) -> bool:
-    return site in ('sf', 'sofurry')
+  @staticmethod
+  def transformer_matches_site(site: str) -> bool:
+    return site in SUPPORTED_USER_TAGS['sofurry']
 
   def user_tag_root(self, data):
-    user_data = data[0]
-    if user_data['sf']:
-      return f':icon{user_data["sf"]}:'
-    if user_data.default is None:
-      for site in user_data.sites:
-        if site == 'fa':
-          return f'fa!{user_data["fa"]}'
-        if site == 'ib':
-          return f'ib!{user_data["ib"]}'
-    return super(SoFurryTransformer, self).user_tag_root(data)
+    user_data: SiteSwitchTag = data[0]
+    if user_data['sofurry']:
+      return f':icon{user_data["sofurry"]}:'
+    for site in user_data.sites:
+      if site == 'furaffinity':
+        return f'fa!{user_data["furaffinity"]}'
+      if site == 'inkbunny':
+        return f'ib!{user_data["inkbunny"]}'
+    return super().user_tag_root(data)
+
+  def siteurl_tag_root(self, data):
+    siteurl_data: SiteSwitchTag = data[0]
+    if 'sofurry' in siteurl_data:
+      return self.url_tag((siteurl_data['sofurry'], siteurl_data.default))
+    return super().siteurl_tag_root(data)
 
 
-def parse_description(description_path, config_path, out_dir, ignore_empty_files=False):
-  ps = subprocess.Popen(('libreoffice', '--cat', description_path), stdout=subprocess.PIPE)
-  description = '\n'.join(line.strip() for line in io.TextIOWrapper(ps.stdout, encoding='utf-8-sig'))
+def validate_parsed_tree(parsed_tree):
+  for node in parsed_tree.iter_subtrees_topdown():
+    if node.data in {'b_tag', 'i_tag', 'u_tag', 'url_tag'}:
+      node_type = str(node.data)
+      for node2 in node.find_data(node_type):
+        if node != node2:
+          raise DescriptionParsingError(f'Invalid nested {node_type} on line {node2.data.line} column {node2.data.column}')
+
+def parse_description(description_path, config, out_dir, ignore_empty_files=False, define_options=set()):
+  for proc in psutil.process_iter(['cmdline']):
+    if proc.info['cmdline'] and 'libreoffice' in proc.info['cmdline'][0] and '--writer' in proc.info['cmdline'][1:]:
+      if ignore_empty_files:
+        print('WARN: LibreOffice Writer appears to be running. This command may output empty files until it is closed.')
+        break
+      print('WARN: LibreOffice Writer appears to be running. This command may raise an error until it is closed.')
+      break
+
+  description = ''
+  with subprocess.Popen(('libreoffice', '--cat', description_path), stdout=subprocess.PIPE) as ps:
+    description = '\n'.join(line.strip() for line in io.TextIOWrapper(ps.stdout, encoding='utf-8-sig'))
   if not description or re.match(r'^\s+$', description):
     error = f'Description processing returned empty file: libreoffice --cat {description_path}'
     if ignore_empty_files:
@@ -360,7 +518,21 @@ def parse_description(description_path, config_path, out_dir, ignore_empty_files
     else:
       raise RuntimeError(error)
 
-  parsed_description = DESCRIPTION_PARSER.parse(description)
+  try:
+    parsed_description = DESCRIPTION_PARSER.parse(description)
+  except lark.UnexpectedInput as e:
+    input_error = e.match_examples(DESCRIPTION_PARSER.parse, {
+      'Unclosed tag': ['[b]text', '[i]text', '[u]text', '[url]text'],
+      'Unopened tag': ['text[/b]', 'text[/i]', 'text[/u]', 'text[/url]'],
+      'Unknown tag': ['[invalid]text[/invalid]'],
+      'Missing tag brackets': ['b]text[/b]', '[btext[/b]', '[b]text/b]', '[b]text[/b', 'i]text[/i]', '[itext[/i]', '[i]text/i]', '[i]text[/i', 'u]text[/u]', '[utext[/u]', '[u]text/u]', '[u]text[/u'],
+      'Missing tag slash': ['[b]text[b]', '[i]text[i]', '[u]text[u]'],
+      'Empty switch tag': ['[user][/user]', '[siteurl][/siteurl]'],
+      'Empty user tag': ['[user][aryion][/aryion][/user]', '[user][furaffinity][/furaffinity][/user]', '[user][inkbunny][/inkbunny][/user]', '[user][sofurry][/sofurry][/user]', '[user][weasyl][/weasyl][/user]', '[user][twitter][/twitter][/user]', '[user][mastodon][/mastodon][/user]', '[user][aryion=][/aryion][/user]', '[user][furaffinity=][/furaffinity][/user]', '[user][inkbunny=][/inkbunny][/user]', '[user][sofurry=][/sofurry][/user]', '[user][weasyl=][/weasyl][/user]', '[user][twitter=][/twitter][/user]', '[user][mastodon=][/mastodon][/user]'],
+      'Empty siteurl tag': ['[siteurl][aryion][/aryion][/siteurl]', '[siteurl][furaffinity][/furaffinity][/siteurl]', '[siteurl][inkbunny][/inkbunny][/siteurl]', '[siteurl][sofurry][/sofurry][/siteurl]', '[siteurl][weasyl][/weasyl][/siteurl]' '[siteurl][aryion=][/aryion][/siteurl]', '[siteurl][furaffinity=][/furaffinity][/siteurl]', '[siteurl][inkbunny=][/inkbunny][/siteurl]', '[siteurl][sofurry=][/sofurry][/siteurl]', '[siteurl][weasyl=][/weasyl][/siteurl]'],
+    })
+    raise DescriptionParsingError(f'Unable to parse description. {input_error or "Unknown grammar error"} in line {e.line} column {e.column}:\n{e.get_context(description)}') from e
+  validate_parsed_tree(parsed_description)
   transformations = {
     'aryion': ('desc_aryion.txt', AryionTransformer),
     'furaffinity': ('desc_furaffinity.txt', FuraffinityTransformer),
@@ -368,31 +540,29 @@ def parse_description(description_path, config_path, out_dir, ignore_empty_files
     'sofurry': ('desc_sofurry.txt', SoFurryTransformer),
     'weasyl': ('desc_weasyl.md', WeasylTransformer),
   }
-  with open(config_path, 'r') as f:
-    config = json.load(f)
+  # assert all(k in SUPPORTED_SITE_TAGS for k in transformations)
   # Validate JSON
   errors = []
-  if type(config) is not dict:
-    errors.append(ValueError('Configuration must be a JSON object'))
-  else:
-    for (website, username) in config.items():
-      if website not in transformations:
-        errors.append(ValueError(f'Website \'{website}\' is unsupported'))
-      elif type(username) is not str:
-        errors.append(ValueError(f'Website \'{website}\' has invalid username \'{json.dumps(username)}\''))
-      elif username.strip() == '':
-        errors.append(ValueError(f'Website \'{website}\' has empty username'))
-    if not any(ws in config for ws in ('aryion', 'furaffinity', 'weasyl', 'inkbunny', 'sofurry')):
-      errors.append(ValueError('No valid websites found'))
+  for (website, username) in config.items():
+    if website not in transformations:
+      errors.append(ValueError(f'Website \'{website}\' is unsupported'))
+    elif type(username) is not str:
+      errors.append(ValueError(f'Website \'{website}\' has invalid username \'{json.dumps(username)}\''))
+    elif username.strip() == '':
+      errors.append(ValueError(f'Website \'{website}\' has empty username'))
+  if not any(ws in config for ws in transformations):
+    errors.append(ValueError('No valid websites found'))
   if errors:
     raise ExceptionGroup('Invalid configuration for description parsing', errors)
   # Create descriptions
-  re_multiple_empty_lines = re.compile(r'\n\n+')
+  RE_MULTIPLE_EMPTY_LINES = re.compile(r'\n\n+')
   for (website, username) in config.items():
     (filepath, transformer) = transformations[website]
     with open(os.path.join(out_dir, filepath), 'w') as f:
       if description.strip():
-        transformed_description = transformer(username).transform(parsed_description)
-        f.write(re_multiple_empty_lines.sub('\n\n', transformed_description))
-      else:
-        f.write('')
+        transformed_description = transformer(self_user=username, define_options=define_options).transform(parsed_description)
+        cleaned_description = RE_MULTIPLE_EMPTY_LINES.sub('\n\n', transformed_description).strip()
+        if cleaned_description:
+          f.write(cleaned_description)
+          f.write('\n')
+      f.write('')
diff --git a/main.py b/main.py
old mode 100644
new mode 100755
index 41cd036..222d403
--- a/main.py
+++ b/main.py
@@ -1,18 +1,47 @@
+#!/usr/bin/env python
+# PYTHON_ARGCOMPLETE_OK
+import argcomplete
+from argcomplete.completers import FilesCompleter, DirectoriesCompleter
 import argparse
+import json
 import os
+import re
 from subprocess import CalledProcessError
 import shutil
 import tempfile
 
 from description import parse_description
 from story import parse_story
+from sites import INVERSE_SUPPORTED_SITE_TAGS
 
 
-def main(out_dir_path=None, story_path=None, description_path=None, file_path=None, config_path=None, keep_out_dir=False, ignore_empty_files=False):
+def main(out_dir_path=None, story_path=None, description_path=None, file_paths=[], config_path=None, keep_out_dir=False, ignore_empty_files=False, define_options=[]):
   if not out_dir_path:
     raise ValueError('Missing out_dir_path')
   if not config_path:
     raise ValueError('Missing config_path')
+  if not file_paths:
+    file_paths = []
+  if not define_options:
+    define_options = []
+  config = None
+  if story_path or description_path:
+    with open(config_path, 'r') as f:
+      config_json = json.load(f)
+    if type(config_json) is not dict:
+      raise ValueError('The configuration file must contain a valid JSON object')
+    config = {}
+    for k, v in config_json.items():
+      if type(v) is not str:
+        raise ValueError(f'Invalid configuration value for entry "{k}": expected string, got {type(v)}')
+      new_k = INVERSE_SUPPORTED_SITE_TAGS.get(k)
+      if not new_k:
+        print(f'Ignoring unknown configuration key "{k}"...')
+      if new_k in config:
+        raise ValueError(f'Duplicate configuration entry for website "{new_key}": found collision with key "{k}"')
+      config[new_k] = v
+    if len(config) == 0:
+      raise ValueError(f'Invalid configuration file "{config_path}": no valid sites defined')
   remove_out_dir = not keep_out_dir and os.path.isdir(out_dir_path)
   with tempfile.TemporaryDirectory() as tdir:
     # Clear output dir if it exists and shouldn't be kept
@@ -24,14 +53,17 @@ def main(out_dir_path=None, story_path=None, description_path=None, file_path=No
     try:
       # Convert original file to .rtf (Aryion) and .txt (all others)
       if story_path:
-        parse_story(story_path, config_path, out_dir_path, tdir, ignore_empty_files)
+        parse_story(story_path, config, out_dir_path, tdir, ignore_empty_files)
 
       # Parse FA description and convert for each website
       if description_path:
-        parse_description(description_path, config_path, out_dir_path, ignore_empty_files)
+        define_options_set = set(define_options)
+        if len(define_options_set) < len(define_options):
+          print('WARNING: duplicated entries defined with -D / --define-option')
+        parse_description(description_path, config, out_dir_path, ignore_empty_files, define_options)
 
-      # Copy generic file over to output
-      if file_path:
+      # Copy generic files over to output
+      for file_path in file_paths:
         shutil.copy(file_path, out_dir_path)
 
     except CalledProcessError as e:
@@ -52,32 +84,41 @@ def main(out_dir_path=None, story_path=None, description_path=None, file_path=No
 if __name__ == '__main__':
   parser = argparse.ArgumentParser(description='generate multi-gallery upload-ready files')
   parser.add_argument('-o', '--output-dir', dest='out_dir_path', default='./out',
-                      help='path of output directory')
+                      help='path of output directory').completer = DirectoriesCompleter
   parser.add_argument('-c', '--config', dest='config_path', default='./config.json',
-                      help='path of JSON configuration file')
+                      help='path of JSON configuration file').completer = FilesCompleter
+  parser.add_argument('-D', '--define-option', dest='define_options', action='append',
+                      help='options to define as a truthy value when parsing descriptions')
   parser.add_argument('-s', '--story', dest='story_path',
-                      help='path of LibreOffice-readable story file')
+                      help='path of LibreOffice-readable story file').completer = FilesCompleter
   parser.add_argument('-d', '--description', dest='description_path',
-                      help='path of BBCode-formatted description file')
-  parser.add_argument('-f', '--file', dest='file_path',
-                      help='path of generic file to include in output (i.e. an image or thumbnail)')
+                      help='path of BBCode-formatted description file').completer = FilesCompleter
+  parser.add_argument('-f', '--file', dest='file_paths', action='append',
+                      help='path(s) of generic file(s) to include in output (i.e. an image or thumbnail)').completer = FilesCompleter
   parser.add_argument('-k', '--keep-out-dir', dest='keep_out_dir', action='store_true',
                       help='whether output directory contents should be kept.\nif set, a script error may leave partial files behind')
   parser.add_argument('-I', '--ignore-empty-files', dest='ignore_empty_files', action='store_true',
                       help='do not raise an error if any input file is empty or whitespace-only')
+  argcomplete.autocomplete(parser)
   args = parser.parse_args()
 
-  if not any([args.story_path, args.description_path]):
-    parser.error('at least one of ( --story | --description ) must be set')
+  file_paths = args.file_paths or []
+  if not (args.story_path or args.description_path or any(file_paths)):
+    parser.error('at least one of ( --story | --description | --file ) must be set')
   if args.out_dir_path and os.path.exists(args.out_dir_path) and not os.path.isdir(args.out_dir_path):
-    parser.error('--output-dir must be an existing directory or inexistent')
+    parser.error(f'--output-dir {args.out_dir_path} must be an existing directory or inexistent; found a file instead')
   if args.story_path and not os.path.isfile(args.story_path):
-    parser.error('--story must be a valid file')
+    parser.error(f'--story {args.story_path} is not a valid file')
   if args.description_path and not os.path.isfile(args.description_path):
-    parser.error('--description must be a valid file')
-  if args.file_path and not os.path.isfile(args.file_path):
-    parser.error('--file must be a valid file')
-  if args.config_path and not os.path.isfile(args.config_path):
+    parser.error(f'--description {args.description_path} is not a valid file')
+  for file_path in file_paths:
+    if not os.path.isfile(file_path):
+      parser.error(f'--file {file_path} is not a valid file')
+  if (args.story_path or args.description_path) and args.config_path and not os.path.isfile(args.config_path):
     parser.error('--config must be a valid file')
+  if args.define_options:
+    for option in args.define_options:
+      if not re.match(r'^[a-zA-Z0-9_-]+$', option):
+        parser.error(f'--define-option {option} is not a valid option; it must only contain alphanumeric characters, dashes, or underlines')
 
   main(**vars(args))
diff --git a/requirements.txt b/requirements.txt
index acc69ce..1a6a9d2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,4 @@
-lark==1.1.5
+argcomplete==3.2.1
+lark==1.1.8
+parameterized==0.9.0
+psutil==5.9.6
diff --git a/sites.py b/sites.py
new file mode 100644
index 0000000..9a2f09c
--- /dev/null
+++ b/sites.py
@@ -0,0 +1,13 @@
+import itertools
+import typing
+
+SUPPORTED_SITE_TAGS: typing.Mapping[str, typing.Set[str]] = {
+  'aryion': {'aryion', 'eka', 'eka_portal'},
+  'furaffinity': {'furaffinity', 'fa'},
+  'weasyl': {'weasyl'},
+  'inkbunny': {'inkbunny', 'ib'},
+  'sofurry': {'sofurry', 'sf'},
+}
+
+INVERSE_SUPPORTED_SITE_TAGS: typing.Mapping[str, str] = \
+  dict(itertools.chain.from_iterable(zip(v, itertools.repeat(k)) for (k, v) in SUPPORTED_SITE_TAGS.items()))
diff --git a/story.py b/story.py
index 911187a..d11b052 100644
--- a/story.py
+++ b/story.py
@@ -1,6 +1,7 @@
 import io
 import json
 import os
+import psutil
 import re
 import subprocess
 
@@ -16,43 +17,57 @@ def get_rtf_styles(rtf_source: str):
     rtf_styles[style_name] = rtf_style
   return rtf_styles
 
-def parse_story(story_path, config_path, out_dir, temp_dir, ignore_empty_files=False):
-  with open(config_path, 'r') as f:
-    config = json.load(f)
-  if type(config) is not dict:
-    raise ValueError('Invalid configuration for story parsing: Configuration must be a JSON object')
-  should_create_txt_story = any(ws in config for ws in ('furaffinity', 'weasyl', 'inkbunny', 'sofurry'))
+def parse_story(story_path, config, out_dir, temp_dir, ignore_empty_files=False):
+  should_create_txt_story = any(ws in config for ws in ('furaffinity', 'inkbunny', 'sofurry'))
+  should_create_md_story = any(ws in config for ws in ('weasyl',))
   should_create_rtf_story = any(ws in config for ws in ('aryion',))
-  if not should_create_txt_story and not should_create_rtf_story:
+  if not (should_create_txt_story or should_create_md_story or should_create_rtf_story):
     raise ValueError('Invalid configuration for story parsing: No valid websites found')
 
+  for proc in psutil.process_iter(['cmdline']):
+    if proc.info['cmdline'] and 'libreoffice' in proc.info['cmdline'][0] and '--writer' in proc.info['cmdline'][1:]:
+      if ignore_empty_files:
+        print('WARN: LibreOffice Writer appears to be running. This command may output empty files until it is closed.')
+        break
+      print('WARN: LibreOffice Writer appears to be running. This command may raise an error until it is closed.')
+      break
+
   story_filename = os.path.split(story_path)[1].rsplit('.')[0]
   txt_out_path = os.path.join(out_dir, f'{story_filename}.txt') if should_create_txt_story else os.devnull
+  md_out_path = os.path.join(out_dir, f'{story_filename}.md') if should_create_md_story else os.devnull
   txt_tmp_path = os.path.join(temp_dir, f'{story_filename}.txt') if should_create_rtf_story else os.devnull
-  RE_EMPTY_LINE = re.compile('^$')
+  RE_EMPTY_LINE = re.compile(r'^$')
+  RE_SEQUENTIAL_EQUAL_SIGNS = re.compile(r'=(?==)')
   is_only_empty_lines = True
-  ps = subprocess.Popen(('libreoffice', '--cat', story_path), stdout=subprocess.PIPE)
-  # Mangle output files so that .RTF will always have a single LF between lines, and .TXT can have one or two CRLF
-  with open(txt_out_path, 'w', newline='\r\n') as txt_out, open(txt_tmp_path, 'w') as txt_tmp:
-    needs_empty_line = False
-    for line in io.TextIOWrapper(ps.stdout, encoding='utf-8-sig'):
-      # Remove empty lines
-      line = line.strip()
-      if RE_EMPTY_LINE.search(line) and not is_only_empty_lines:
-        needs_empty_line = True
-      else:
-        if is_only_empty_lines:
-          txt_out.writelines((line,))
-          txt_tmp.writelines((line,))
-          is_only_empty_lines = False
+  with subprocess.Popen(('libreoffice', '--cat', story_path), stdout=subprocess.PIPE) as ps:
+    # Mangle output files so that .RTF will always have a single LF between lines, and .TXT/.MD can have one or two CRLF
+    with open(txt_out_path, 'w', newline='\r\n') as txt_out, open(md_out_path, 'w', newline='\r\n') as md_out, open(txt_tmp_path, 'w') as txt_tmp:
+      needs_empty_line = False
+      for line in io.TextIOWrapper(ps.stdout, encoding='utf-8-sig'):
+        # Remove empty lines
+        line = line.strip()
+        md_line = line
+        if RE_EMPTY_LINE.search(line) and not is_only_empty_lines:
+          needs_empty_line = True
         else:
-          if needs_empty_line:
-            txt_out.writelines(('\n\n', line))
-            needs_empty_line = False
+          if should_create_md_story:
+            md_line = RE_SEQUENTIAL_EQUAL_SIGNS.sub('= ', line.replace(r'*', r'\*'))
+          if is_only_empty_lines:
+            txt_out.writelines((line,))
+            md_out.writelines((md_line,))
+            txt_tmp.writelines((line,))
+            is_only_empty_lines = False
           else:
-            txt_out.writelines(('\n', line))
-          txt_tmp.writelines(('\n', line))
-    txt_out.writelines(('\n'))
+            if needs_empty_line:
+              txt_out.writelines(('\n\n', line))
+              md_out.writelines(('\n\n', md_line))
+              needs_empty_line = False
+            else:
+              txt_out.writelines(('\n', line))
+              md_out.writelines(('\n', md_line))
+            txt_tmp.writelines(('\n', line))
+      txt_out.writelines(('\n'))
+      md_out.writelines(('\n'))
   if is_only_empty_lines:
     error = f'Story processing returned empty file: libreoffice --cat {story_path}'
     if ignore_empty_files:
diff --git a/test.py b/test.py
new file mode 100644
index 0000000..0a3bbb9
--- /dev/null
+++ b/test.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+import glob
+import os.path
+from parameterized import parameterized
+import re
+import tempfile
+import unittest
+import warnings
+
+from description import parse_description, DescriptionParsingError
+
+class TestParseDescription(unittest.TestCase):
+  config = {
+    'aryion': 'UserAryion',
+    'furaffinity': 'UserFuraffinity',
+    'inkbunny': 'UserInkbunny',
+    'sofurry': 'UserSoFurry',
+    'weasyl': 'UserWeasyl',
+  }
+  define_options = {'test_parse_description'}
+
+  def setUp(self):
+    self.tmpdir = tempfile.TemporaryDirectory(ignore_cleanup_errors=True)
+    warnings.simplefilter('ignore', ResourceWarning)
+
+  def tearDown(self):
+    self.tmpdir.cleanup()
+    warnings.simplefilter('default', ResourceWarning)
+
+  @parameterized.expand([
+    (re.match(r'.*(input_\d+)\.txt', v)[1], v) for v in sorted(glob.iglob('./test/description/input_*.txt'))
+  ])
+  def test_parse_success(self, name, test_description):
+    with tempfile.TemporaryDirectory(ignore_cleanup_errors=True) as tmpdir:
+      parse_description(test_description, self.config, tmpdir, define_options=self.define_options)
+      for expected_output_file in glob.iglob(f'./test/description/output_{name[6:]}/*'):
+        received_output_file = os.path.join(tmpdir, os.path.split(expected_output_file)[1])
+        self.assertTrue(os.path.exists(received_output_file))
+        self.assertTrue(os.path.isfile(received_output_file))
+        with open(received_output_file, 'r') as f:
+          received_description = f.read()
+        with open(expected_output_file, 'r') as f:
+          expected_description = f.read()
+        self.assertEqual(received_description, expected_description)
+
+  @parameterized.expand([
+    (re.match(r'.*(error_.+)\.txt', v)[1], v) for v in sorted(glob.iglob('./test/description/error_*.txt'))
+  ])
+  def test_parse_errors(self, _, test_description):
+    self.assertRaises(DescriptionParsingError, lambda: parse_description(test_description, self.config, self.tmpdir.name, define_options=self.define_options))
+    self.assertListEqual(glob.glob(os.path.join(self.tmpdir.name, '*')), [])
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/test/description/error_1_nested_url_tag.txt b/test/description/error_1_nested_url_tag.txt
new file mode 100644
index 0000000..02edf64
--- /dev/null
+++ b/test/description/error_1_nested_url_tag.txt
@@ -0,0 +1 @@
+[url=https://example.com]Nested [url=https://example.net]URLs[/url][/url]
diff --git a/test/description/error_2_deeply_nested_b_tag.txt b/test/description/error_2_deeply_nested_b_tag.txt
new file mode 100644
index 0000000..8ca1142
--- /dev/null
+++ b/test/description/error_2_deeply_nested_b_tag.txt
@@ -0,0 +1 @@
+ZERO[b]ONE[i]TWO[u]THREE[b]FOUR[url=https://example.com]FIVE[/url]FOUR[/b]THREE[/u]TWO[/i]ONE[/b]ZERO
diff --git a/test/description/error_3_unclosed_i_tag.txt b/test/description/error_3_unclosed_i_tag.txt
new file mode 100644
index 0000000..6cab7b4
--- /dev/null
+++ b/test/description/error_3_unclosed_i_tag.txt
@@ -0,0 +1 @@
+[i]Hello world!
diff --git a/test/description/error_4_unopened_u_tag.txt b/test/description/error_4_unopened_u_tag.txt
new file mode 100644
index 0000000..038f01c
--- /dev/null
+++ b/test/description/error_4_unopened_u_tag.txt
@@ -0,0 +1 @@
+Hello world![/u]
diff --git a/test/description/error_5_unknown_user_tag.txt b/test/description/error_5_unknown_user_tag.txt
new file mode 100644
index 0000000..84935a7
--- /dev/null
+++ b/test/description/error_5_unknown_user_tag.txt
@@ -0,0 +1 @@
+[user][unknown=Foo]Bar[/unknown][/user]
diff --git a/test/description/input_1.txt b/test/description/input_1.txt
new file mode 100644
index 0000000..5e8ee39
--- /dev/null
+++ b/test/description/input_1.txt
@@ -0,0 +1,9 @@
+[b]Hello world![/b]
+
+This is just a [u]simple[/u] test to show that basic functionality of [url=https://github.com/BadMannersXYZ/upload-generator]upload-generator[/url] [i]works[/i]. [if=define==test_parse_description]And this is running in a unit test.[/if][else]Why did you parse this outside of a unit test?![/else]
+
+[center]Reminder that I am [self][/self]![/center]
+
+My friend: [user][sofurry=FriendSoFurry][fa=FriendFa][mastodon=@FriendMastodon@example.org]Friend123[/mastodon][/fa][/sofurry][/user][if=site in ib,aryion,weasyl] (I dunno his account here...)[/if]
+
+[siteurl][eka=https://example.com/eka][inkbunny=https://example.com/ib][generic=https://example.com/generic]Check this page![/generic][/inkbunny][/eka][/siteurl]
diff --git a/test/description/input_2.txt b/test/description/input_2.txt
new file mode 100644
index 0000000..71385df
--- /dev/null
+++ b/test/description/input_2.txt
@@ -0,0 +1,12 @@
+[self][/self]
+
+[if=site==eka] -> [/if][user][eka=EkaPerson]EkaName[/eka][/user] [user][eka]EkaPerson[/eka][/user]
+[if=site==fa] -> [/if][user][fa=FaPerson]FaName[/fa][/user] [user][fa]FaPerson[/fa][/user]
+[if=site==ib] -> [/if][user][ib=IbPerson]IbName[/ib][/user] [user][ib]IbPerson[/ib][/user]
+[if=site==sofurry] -> [/if][user][sf=SfPerson]SfName[/sf][/user] [user][sf]SfPerson[/sf][/user]
+[if=site==weasyl] -> [/if][user][weasyl=WeasylPerson]WeasylName[/weasyl][/user] [user][weasyl]WeasylPerson[/weasyl][/user]
+[user][twitter=XPerson]XName[/twitter][/user] [user][twitter]XPerson[/twitter][/user]
+[user][mastodon=MastodonPerson@example.com]MastodonName[/mastodon][/user] [user][mastodon]MastodonPerson@example.com[/mastodon][/user]
+[user][twitter=Ignored][generic=https://example.net/GenericPerson]GenericName[/generic][/twitter][/user]
+
+[siteurl][aryion=https://example.com/aryion][furaffinity=https://example.com/furaffinity][inkbunny=https://example.com/inkbunny][sofurry=https://example.com/sofurry][generic=https://example.com/generic]Link[/generic][/sofurry][/inkbunny][/furaffinity][/aryion][/siteurl]
diff --git a/test/description/output_1/desc_aryion.txt b/test/description/output_1/desc_aryion.txt
new file mode 100644
index 0000000..3cd68c2
--- /dev/null
+++ b/test/description/output_1/desc_aryion.txt
@@ -0,0 +1,9 @@
+[b]Hello world![/b]
+
+This is just a [u]simple[/u] test to show that basic functionality of [url=https://github.com/BadMannersXYZ/upload-generator]upload-generator[/url] [i]works[/i]. And this is running in a unit test.
+
+[center]Reminder that I am :iconUserAryion:![/center]
+
+My friend: [url=https://example.org/@FriendMastodon]Friend123[/url] (I dunno his account here...)
+
+[url=https://example.com/eka]Check this page![/url]
diff --git a/test/description/output_1/desc_furaffinity.txt b/test/description/output_1/desc_furaffinity.txt
new file mode 100644
index 0000000..3faa943
--- /dev/null
+++ b/test/description/output_1/desc_furaffinity.txt
@@ -0,0 +1,9 @@
+[b]Hello world![/b]
+
+This is just a [u]simple[/u] test to show that basic functionality of [url=https://github.com/BadMannersXYZ/upload-generator]upload-generator[/url] [i]works[/i]. And this is running in a unit test.
+
+[center]Reminder that I am :iconUserFuraffinity:![/center]
+
+My friend: :iconFriendFa:
+
+[url=https://example.com/generic]Check this page![/url]
diff --git a/test/description/output_1/desc_inkbunny.txt b/test/description/output_1/desc_inkbunny.txt
new file mode 100644
index 0000000..1575e9a
--- /dev/null
+++ b/test/description/output_1/desc_inkbunny.txt
@@ -0,0 +1,9 @@
+[b]Hello world![/b]
+
+This is just a [u]simple[/u] test to show that basic functionality of [url=https://github.com/BadMannersXYZ/upload-generator]upload-generator[/url] [i]works[/i]. And this is running in a unit test.
+
+[center]Reminder that I am [iconname]UserInkbunny[/iconname]![/center]
+
+My friend: [fa]FriendFa[/fa] (I dunno his account here...)
+
+[url=https://example.com/ib]Check this page![/url]
diff --git a/test/description/output_1/desc_sofurry.txt b/test/description/output_1/desc_sofurry.txt
new file mode 100644
index 0000000..f677efd
--- /dev/null
+++ b/test/description/output_1/desc_sofurry.txt
@@ -0,0 +1,9 @@
+[b]Hello world![/b]
+
+This is just a [u]simple[/u] test to show that basic functionality of [url=https://github.com/BadMannersXYZ/upload-generator]upload-generator[/url] [i]works[/i]. And this is running in a unit test.
+
+[center]Reminder that I am :iconUserSoFurry:![/center]
+
+My friend: :iconFriendSoFurry:
+
+[url=https://example.com/generic]Check this page![/url]
diff --git a/test/description/output_1/desc_weasyl.md b/test/description/output_1/desc_weasyl.md
new file mode 100644
index 0000000..d950166
--- /dev/null
+++ b/test/description/output_1/desc_weasyl.md
@@ -0,0 +1,9 @@
+**Hello world!**
+
+This is just a <u>simple</u> test to show that basic functionality of [upload-generator](https://github.com/BadMannersXYZ/upload-generator) *works*. And this is running in a unit test.
+
+<div class="align-center">Reminder that I am <!~UserWeasyl>!</div>
+
+My friend: <fa:FriendFa> (I dunno his account here...)
+
+[Check this page!](https://example.com/generic)
diff --git a/test/description/output_2/desc_aryion.txt b/test/description/output_2/desc_aryion.txt
new file mode 100644
index 0000000..89e6c3b
--- /dev/null
+++ b/test/description/output_2/desc_aryion.txt
@@ -0,0 +1,12 @@
+:iconUserAryion:
+
+ -> :iconEkaPerson: :iconEkaPerson:
+[url=https://furaffinity.net/user/FaPerson]FaName[/url] [url=https://furaffinity.net/user/FaPerson]FaPerson[/url]
+[url=https://inkbunny.net/IbPerson]IbName[/url] [url=https://inkbunny.net/IbPerson]IbPerson[/url]
+[url=https://sfperson.sofurry.com]SfName[/url] [url=https://sfperson.sofurry.com]SfPerson[/url]
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/aryion]Link[/url]
diff --git a/test/description/output_2/desc_furaffinity.txt b/test/description/output_2/desc_furaffinity.txt
new file mode 100644
index 0000000..69f338f
--- /dev/null
+++ b/test/description/output_2/desc_furaffinity.txt
@@ -0,0 +1,12 @@
+:iconUserFuraffinity:
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+ -> :iconFaPerson: :iconFaPerson:
+[url=https://inkbunny.net/IbPerson]IbName[/url] [url=https://inkbunny.net/IbPerson]IbPerson[/url]
+[url=https://sfperson.sofurry.com]SfName[/url] [url=https://sfperson.sofurry.com]SfPerson[/url]
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/furaffinity]Link[/url]
diff --git a/test/description/output_2/desc_inkbunny.txt b/test/description/output_2/desc_inkbunny.txt
new file mode 100644
index 0000000..52eafb8
--- /dev/null
+++ b/test/description/output_2/desc_inkbunny.txt
@@ -0,0 +1,12 @@
+[iconname]UserInkbunny[/iconname]
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+[fa]FaPerson[/fa] [fa]FaPerson[/fa]
+ -> [iconname]IbPerson[/iconname] [iconname]IbPerson[/iconname]
+[sf]SfPerson[/sf] [sf]SfPerson[/sf]
+[weasyl]weasylperson[/weasyl] [weasyl]weasylperson[/weasyl]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/inkbunny]Link[/url]
diff --git a/test/description/output_2/desc_sofurry.txt b/test/description/output_2/desc_sofurry.txt
new file mode 100644
index 0000000..505deb3
--- /dev/null
+++ b/test/description/output_2/desc_sofurry.txt
@@ -0,0 +1,12 @@
+:iconUserSoFurry:
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+fa!FaPerson fa!FaPerson
+ib!IbPerson ib!IbPerson
+ -> :iconSfPerson: :iconSfPerson:
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/sofurry]Link[/url]
diff --git a/test/description/output_2/desc_weasyl.md b/test/description/output_2/desc_weasyl.md
new file mode 100644
index 0000000..10d2e42
--- /dev/null
+++ b/test/description/output_2/desc_weasyl.md
@@ -0,0 +1,12 @@
+<!~UserWeasyl>
+
+[EkaName](https://aryion.com/g4/user/EkaPerson) [EkaPerson](https://aryion.com/g4/user/EkaPerson)
+<fa:FaPerson> <fa:FaPerson>
+<ib:IbPerson> <ib:IbPerson>
+<sf:SfPerson> <sf:SfPerson>
+ -> <!~WeasylPerson> <!~WeasylPerson>
+[XName](https://twitter.com/XPerson) [XPerson](https://twitter.com/XPerson)
+[MastodonName](https://example.com/@MastodonPerson) [MastodonPerson@example.com](https://example.com/@MastodonPerson)
+[GenericName](https://example.net/GenericPerson)
+
+[Link](https://example.com/generic)