Add tc-tag-missing or tc-tag-exists to tag pills including docs (#7951)

* add tc-tag-missing or tc-tag-exists to tag pills including docs

* changes as requested

* macros not needed anymore - so remove

* fix the tag Macro docs

core/wiki/macros/tag.tid

@@ -21,7 +21,9 @@ color:$(foregroundColor)$;
 >
 	<<__actions__>>
 	<$transclude tiddler=<<__icon__>>/>
-	<$view tiddler=<<__tag__>> field="title" format="text" />
+	<span class={{{ [<__tag__>is[missing]then[tc-tag-missing]else[tc-tag-exists]] }}}>
+		<$view tiddler=<<__tag__>> field="title" format="text" />
+	</span>
 </$element-tag$>
 </$let>
 \end

editions/tw5.com/tiddlers/macros/TagMacro.tid

@@ -1,6 +1,6 @@
 caption: tag
 created: 20141206130540337
-modified: 20230725201240201
+modified: 20240228131301798
 tags: Macros [[Core Macros]]
 title: tag Macro
 type: text/vnd.tiddlywiki
@@ -11,7 +11,35 @@ The <<.def tag>> [[macro|Macros]] generates a tag pill for a specified tag. Clic
 
 !! Parameters
 
-;tag
+; tag
 : The title of the tag, defaulting to the [[current tiddler|Current Tiddler]]
 
+!! CSS classes
+
+<<.from-version "v5.3.4">>
+
+; `tc-tag-missing`
+: This class is defined if a tag does ''not exist'' as a tiddler.
+
+; `tc-tag-exists`
+: This class is defined if a tag does exist as a tiddler
+
+!!! Defining the class
+
+To define the `tc-tag-missing` class a stylesheet tiddler needs to be created. The default font-style for missing tiddler links is //italic//, so it's used for the example code below. Eg:
+
+''title:'' `myTagsStylesheet`<br>
+''tag:'' `$:/tags/Stylesheet`
+
+<<copy-to-clipboard-above-right src:"""
+.tc-tag-missing {
+	font-style: italic;
+}
+""">>
+```
+.tc-tag-missing {
+	font-style: italic;
+}
+```
+
 <<.macro-examples "tag">>

editions/tw5.com/tiddlers/macros/examples/tag.tid

@@ -1,5 +1,5 @@
 created: 20150221211317000
-modified: 20230725203751870
+modified: 20240228131331605
 tags: [[tag Macro]] [[Macro Examples]]
 title: tag Macro (Examples)
 type: text/vnd.tiddlywiki
@@ -7,22 +7,26 @@ type: text/vnd.tiddlywiki
 <$macrocall $name=".example" n="1" eg="""<<tag>>"""/>
 <$macrocall $name=".example" n="2" eg="""<<tag Concepts>>"""/>
 
+The Following tag can be shown with a font-style: //italic// if the corresponding stylesheet exists. See: [[tag Macro]]
+
+<$macrocall $name=".example" n="3" eg="""<<tag "Does not exist">>"""/>
+
 If a [[list widget|ListWidget]] generates multiple tag macros for the same tag, clicking any of them opens dropdowns on all of them, as in the example below. This is usually unwanted.
-<$macrocall $name=".example" n="3" eg="""<$list filter="[tag[HelloThere]]">
+<$macrocall $name=".example" n="4" eg="""<$list filter="[tag[HelloThere]]">
 
 * <$link/> is tagged with: <$list filter="[<currentTiddler>tags[]]"> <<tag>> </$list>
 
 </$list>"""/>
 
 Adding the `counter="transclusion"` attribute to the list widget that generates multiple identical tag macros causes each of them to be identified as a unique one. Clicking on any of them opens only a single dropdown.
-<$macrocall $name=".example" n="4" eg="""<$list filter="[tag[HelloThere]]" counter="transclusion">
+<$macrocall $name=".example" n="5" eg="""<$list filter="[tag[HelloThere]]" counter="transclusion">
 
 * <$link/> is tagged with: <$list filter="[<currentTiddler>tags[]]"> <<tag>> </$list>
 
 </$list>"""/>
 
 A slightly more performant option is to use the `variable="transclusion"` attribute in the list widget. In this case, the variable `<<transclusion>>` has to be used inside the list widget instead of the `<<currentTiddler>>` .
-<$macrocall $name=".example" n="5" eg="""<$list filter="[tag[HelloThere]]" variable="transclusion">
+<$macrocall $name=".example" n="6" eg="""<$list filter="[tag[HelloThere]]" variable="transclusion">
 
 * <$link to=<<transclusion>>/> is tagged with: <$list filter="[<transclusion>tags[]]"> <<tag>> </$list>