Remove unused GLFM example extension annotations

- These are currently unused, so lets omit them until
  they are needed. Probably when we start doing
  conformance testing.
- Also adds a bit of docs around this. More detailed
  docs will be added in future MRs.

doc/development/gitlab_flavored_markdown/specification_guide/index.md

@@ -653,6 +653,10 @@ is the manually updated canonical Markdown+HTML examples for GLFM extensions.
 
 - It contains examples in the [standard backtick-delimited `spec.txt` format](#various-markdown-specifications),
   each of which contain a Markdown example and the corresponding canonical HTML.
+- For all GitLab examples, the "extension" annotation after the backticks should consist of only
+  `example gitlab`. It does not currently include any additional extension annotations describing
+  the specific Markdown, unlike the GitHub Flavored Markdown examples, which do include
+  these additional annotations (such as `example strikethrough`).
 - The `update-specification.rb` script inserts it as new sections before the appendix
   of generated `spec.txt`.
 - It should consist of `H1` header sections, with all examples nested either 2 or 3 levels deep
@@ -672,7 +676,7 @@ The actual file should not have these prefixed `|` characters.
 |
 |## Strong but with two asterisks
 |
-|```````````````````````````````` example
+|```````````````````````````````` example gitlab
 |**bold**
 |.
 |<p><strong>bold</strong></p>
@@ -682,7 +686,7 @@ The actual file should not have these prefixed `|` characters.
 |
 |## Strong but with HTML
 |
-|```````````````````````````````` example
+|```````````````````````````````` example gitlab
 |<strong>
 |bold
 |</strong>

glfm_specification/input/gitlab_flavored_markdown/glfm_canonical_examples.txt

@@ -13,7 +13,7 @@ examples may be split into multiple top-level headings in the future.
 See
 [the footnotes section of the user-facing documentation for GitLab Flavored Markdown](https://docs.gitlab.com/ee/user/markdown.html#footnotes).
 
-```````````````````````````````` example gitlab footnote
+```````````````````````````````` example gitlab
 footnote reference tag [^fortytwo]
 
 [^fortytwo]: footnote text
@@ -55,7 +55,7 @@ The following are some basic examples; more examples may be added in the future.
 
 Incomplete task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [ ] incomplete
 .
 <ul>
@@ -69,7 +69,7 @@ incomplete
 
 Completed task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [x] completed
 .
 <ul>
@@ -83,7 +83,7 @@ completed
 
 Inapplicable task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [~] inapplicable
 .
 <ul>
@@ -100,7 +100,7 @@ inapplicable
 Inapplicable task in a "loose" list. Note that the `<del>` tag is not applied to the
 loose text; it has strikethrough applied with CSS.
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [~] inapplicable
 
   text in loose list
@@ -131,7 +131,7 @@ This data can be used by static site generators like Jekyll, Hugo, and many othe
 
 YAML front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 ---
 title: YAML front matter
 ---
@@ -145,7 +145,7 @@ title: YAML front matter
 
 TOML front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 +++
 title: TOML front matter
 +++
@@ -159,7 +159,7 @@ title: TOML front matter
 
 JSON front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 ;;;
 {
   "title": "JSON front matter"
@@ -177,7 +177,7 @@ JSON front matter:
 
 Front matter blocks should be inserted at the top of the document:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 text
 
 ---
@@ -191,7 +191,7 @@ title: YAML front matter
 
 Front matter block delimiters shouldn’t be preceded by space characters:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
  ---
 title: YAML front matter
 ---

glfm_specification/output/spec.txt

@@ -9615,7 +9615,7 @@ examples may be split into multiple top-level headings in the future.
 See
 [the footnotes section of the user-facing documentation for GitLab Flavored Markdown](https://docs.gitlab.com/ee/user/markdown.html#footnotes).
 
-```````````````````````````````` example gitlab footnote
+```````````````````````````````` example gitlab
 footnote reference tag [^fortytwo]
 
 [^fortytwo]: footnote text
@@ -9657,7 +9657,7 @@ The following are some basic examples; more examples may be added in the future.
 
 Incomplete task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [ ] incomplete
 .
 <ul>
@@ -9671,7 +9671,7 @@ incomplete
 
 Completed task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [x] completed
 .
 <ul>
@@ -9685,7 +9685,7 @@ completed
 
 Inapplicable task:
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [~] inapplicable
 .
 <ul>
@@ -9702,7 +9702,7 @@ inapplicable
 Inapplicable task in a "loose" list. Note that the `<del>` tag is not applied to the
 loose text; it has strikethrough applied with CSS.
 
-```````````````````````````````` example gitlab tasklist
+```````````````````````````````` example gitlab
 - [~] inapplicable
 
   text in loose list
@@ -9733,7 +9733,7 @@ This data can be used by static site generators like Jekyll, Hugo, and many othe
 
 YAML front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 ---
 title: YAML front matter
 ---
@@ -9747,7 +9747,7 @@ title: YAML front matter
 
 TOML front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 +++
 title: TOML front matter
 +++
@@ -9761,7 +9761,7 @@ title: TOML front matter
 
 JSON front matter:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 ;;;
 {
   "title": "JSON front matter"
@@ -9779,7 +9779,7 @@ JSON front matter:
 
 Front matter blocks should be inserted at the top of the document:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
 text
 
 ---
@@ -9793,7 +9793,7 @@ title: YAML front matter
 
 Front matter block delimiters shouldn’t be preceded by space characters:
 
-```````````````````````````````` example gitlab frontmatter
+```````````````````````````````` example gitlab
  ---
 title: YAML front matter
 ---

spec/scripts/lib/glfm/parse_examples_spec.rb

@@ -74,7 +74,7 @@
 
       ## 2.1.0 H2
 
-      ```````````````````````````````` example gitlab extension_2.1.0-1
+      ```````````````````````````````` example gitlab
       example 6 md
       .
       html
@@ -220,7 +220,7 @@
             disabled: false,
             end_line: 69,
             example: 6,
-            extensions: %w[gitlab extension_2.1.0-1],
+            extensions: %w[gitlab],
             headers: [
               '2.0.0 New H1',
               '2.1.0 H2'

spec/scripts/lib/glfm/update_example_snapshots_spec.rb

@@ -128,7 +128,7 @@
 
       ## Strong but with two asterisks
 
-      ```````````````````````````````` example gitlab strong
+      ```````````````````````````````` example gitlab
       **bold**
       .
       <p><strong>bold</strong></p>
@@ -155,7 +155,7 @@
       `source_specification` will be `gitlab`.
 
 
-      ```````````````````````````````` example gitlab strong
+      ```````````````````````````````` example gitlab
       <strong>
       bold
       </strong>
@@ -169,7 +169,7 @@
 
       ## Strong but skipped
 
-      ```````````````````````````````` example gitlab strong
+      ```````````````````````````````` example gitlab
       **this example will be skipped**
       .
       <p><strong>this example will be skipped</strong></p>
@@ -177,7 +177,7 @@
 
       ## Strong but manually modified and skipped
 
-      ```````````````````````````````` example gitlab strong
+      ```````````````````````````````` example gitlab
       **This example will have its manually modified static HTML, WYSIWYG HTML, and ProseMirror JSON preserved**
       .
       <p><strong>This example will have its manually modified static HTML, WYSIWYG HTML, and ProseMirror JSON preserved</strong></p>