Plugin library chooser improvements

* Make "Also requires:" translatable
* Clearer styling for sub-plugins
* Documentation tweaks

core/language/en-GB/ControlPanel.multids

@@ -63,6 +63,7 @@ Parsing/Pragma/Caption: Pragma Parse Rules
 Plugins/Add/Caption: Get more plugins
 Plugins/Add/Hint: Install plugins from the official library
 Plugins/AlreadyInstalled/Hint: This plugin is already installed at version <$text text=<<installedVersion>>/>
+Plugins/AlsoRequires: Also requires:
 Plugins/Caption: Plugins
 Plugins/Disable/Caption: disable
 Plugins/Disable/Hint: Disable this plugin when reloading page

core/ui/ControlPanel/Modals/AddPlugins.tid

@@ -67,7 +67,7 @@ $:/state/add-plugin-info/$(connectionTiddler)$/$(assetInfo)$
 <$set name="currentTiddler" value=<<assetInfo>>>
 <$list filter="[enlist{!!dependents}] [<currentTiddler>get[parent-plugin]] +[limit[1]]" variable="ignore">
 <div>
-Also requires:
+{{$:/language/ControlPanel/Plugins/AlsoRequires}}
 <$list filter="[enlist{!!dependents}] [{!!parent-plugin}] +[sort[title]]" variable="dependency">
 <$text text=<<dependency>>/>
 </$list>

editions/tw5.com/tiddlers/Plugin Dependencies.tid

@@ -0,0 +1,13 @@
+created: 20190928081852771
+modified: 20190928082758674
+tags: PluginMechanism
+title: Plugin Dependencies
+type: text/vnd.tiddlywiki
+
+The simplest form of dependency between plugins is that one plugin can declare itself to be a sub-plugin of another plugin by specifying that plugin in the `parent-plugin` [[field|Plugin Fields]]. Sub-plugins are displayed in the control panel plugin chooser within the expandable area of their parent plugin. For example, the official plugin library includes the [[CodeMirror Plugin]] and also more than a dozen sub-plugins that extend the CodeMirror plugin with optional functionality. Note that sub-plugins cannot themselves have further sub-plugins.
+
+Plugins can also use their `dependents` [[field|Plugin Fields]] to list the titles of any other plugins that should also be installed. Note that the list is not resolved recursively: dependents of dependents will not be installed.
+
+When installing a plugin from the plugin library, both the `parent-plugin` and `dependents` fields are used to determine any additional plugins to be installed.
+
+Note that the `dependents` field is also used by the ThemeMechanism and the LanguageMechanism to switch in dependent theme/language plugins.

editions/tw5.com/tiddlers/Plugin Types.tid

@@ -0,0 +1,18 @@
+created: 20190928081810311
+modified: 20190928081811355
+tags: 
+title: Plugin Types
+type: text/vnd.tiddlywiki
+
+Plugins have a `plugin-type` field that determines how it is treated. The following values are defined by the core:
+
+* `plugin` - an ordinary plugin
+* `theme` - a theme plugin (see ThemeMechanism). Only the theme plugin named in the tiddler $:/theme is activated at any one time (along with any dependent theme plugins)
+* `language` - a language plugin (see TranslationMechanism). Only the language plugin named in the tiddler $:/language is activated at any one time (along with any dependent language plugins)
+
+The following plugin types are used internally by the core:
+
+* `import` - for the special $:/Import plugin created while importing is in progress
+* `info` - for the special $:/temp/info-plugin tiddler created by the InfoMechanism
+
+While not supported by the plugin library, it is also possible to use custom plugin types to build plugin-like behaviour with a custom user interface. Plugins with a custom type will automatically receive the same behaviour as plain plugins but can display a custom user interface using an appropriate [[view template segment|SystemTag: $:/tags/ViewTemplate]].

editions/tw5.com/tiddlers/mechanisms/PluginMechanism.tid

@@ -1,5 +1,5 @@
 created: 20130826122000000
-modified: 20190927172137277
+modified: 20190928082000464
 tags: Mechanisms
 title: PluginMechanism
 type: text/vnd.tiddlywiki
@@ -16,20 +16,21 @@ By convention, plugin titles have the form `$:/plugins/<publisher>/<name>`. Plug
 
 When [[running TiddlyWiki under Node.js|TiddlyWiki on Node.js]], plugins can also be stored as individual tiddler files in [[PluginFolders]].
 
-Plugins have a `plugin-type` field that determines how it is treated. The following values are defined by the core:
+! Plugin Types
 
-* `plugin` - an ordinary plugin
-* `theme` - a theme plugin (see ThemeMechanism). Only the theme plugin named in the tiddler $:/theme is activated at any one time (along with any dependent theme plugins)
-* `language` - a language plugin (see TranslationMechanism). Only the language plugin named in the tiddler $:/language is activated at any one time (along with any dependent language plugins)
+{{Plugin Types}}
 
-The following plugin types are used internally by the core:
+! Plugin Dependencies
 
-* `import` - for the special $:/Import plugin created while importing is in progress
-* `info` - for the special $:/temp/info-plugin tiddler created by the InfoMechanism
+{{Plugin Dependencies}}
 
-Custom plugin types can also be used. They will automatically receive the same behaviour as plain plugins but can display a custom user interface using an appropriate [[view template segment|SystemTag: $:/tags/ViewTemplate]].
+! Plugin Ordering
 
-See [[Plugin Fields]] for details of the other fields used by plugins.
+{{Plugin Ordering}}
+
+! Plugin Fields
+
+{{Plugin Fields}}
 
 ! More information
 

editions/tw5.com/tiddlers/plugins/Plugin_Fields.tid

@@ -1,11 +1,9 @@
 created: 20161015122718559
-modified: 20190927172655698
+modified: 20190928083018378
 tags: PluginMechanism
 title: Plugin Fields
 type: text/vnd.tiddlywiki
 
-! Plugin fields
-
 Plugins are stored as tiddlers with the following fields:
 
 |!Field |!Description |
@@ -14,6 +12,7 @@ Plugins are stored as tiddlers with the following fields:
 |description |Description of plugin |
 |list |Names of exposed plugin information tiddlers (see below) |
 |name |Brief name of the plugin |
+|plugin-priority |//(optional)// Numerical priority (higher numbers install later, the core plugin has a priority of zero |
 |plugin-type |Generally ''plugin'', ''language'' or ''theme''; see PluginMechanism for details |
 |parent-plugin |//(optional)// <<.from-version "5.1.22">> Title of the plugin under which this plugin should be displayed as a sub-plugin in the control panel plugin chooser |
 |source |//(optional)// Source URL of plugin |

themes/tiddlywiki/vanilla/base.tid

@@ -2179,7 +2179,12 @@ a.tc-tiddlylink.tc-plugin-info:hover .tc-plugin-info > .tc-plugin-info-chunk > s
 }
 
 .tc-plugin-info-dropdown-body {
-	padding: 1em 1em 1em 1em;
+	padding: 1em 1em 0 1em;
+}
+
+.tc-plugin-info-sub-plugins {
+	padding-top: 0.5em;
+	background: <<colour message-background>>;
 }
 
 .tc-plugin-library-listing .tc-install-plugin {