More documentation of extensions

README

@@ -853,7 +853,7 @@ wrapping). Consider, for example:
 
 ### Header identifiers in HTML, LaTeX, and ConTeXt ###
 
-**Extension**
+**Extension: `header_identifiers`**
 
 Each header element in pandoc's HTML and ConTeXt output is given a
 unique identifier. This identifier is based on the text of the header.
@@ -1205,7 +1205,7 @@ If default list markers are desired, use `#.`:
 
 ### Definition lists ###
 
-*Extension*.
+**Extension: `definition_lists`**
 
 Pandoc supports definition lists, using a syntax inspired by
 [PHP Markdown Extra] and [reStructuredText]:[^3]
@@ -1250,7 +1250,7 @@ definition and the next term:
 
 ### Numbered example lists ###
 
-*Extension*.
+**Extension: `example_lists`**
 
 The special list marker `@` can be used for sequentially numbered
 examples. The first list item with a `@` marker will be numbered '1',
@@ -1352,14 +1352,14 @@ A line containing a row of three or more `*`, `-`, or `_` characters
 Tables
 ------
 
-*Extension*.
-
 Four kinds of tables may be used. The first three kinds presuppose the use of
 a fixed-width font, such as Courier. The fourth kind can be used with
 proportionally spaced fonts, as it does not require lining up columns.
 
 ### Simple tables
 
+**Extension: `simple_tables`**
+
 Simple tables look like this:
 
       Right     Left     Center     Default
@@ -1407,6 +1407,8 @@ would be right, left, center, and right aligned, respectively.
 
 ### Multiline tables
 
+**Extension: `multiline_tables`**
+
 Multiline tables allow headers and table rows to span multiple lines
 of text (but cells that span multiple columns or rows of the table are
 not supported).  Here is an example:
@@ -1457,6 +1459,8 @@ the table), or the table may be interpreted as a simple table.
 
 ### Grid tables
 
+**Extension: `grid_tables`**
+
 Grid tables look like this:
 
     : Sample grid table.
@@ -1481,6 +1485,8 @@ columns or rows. Grid tables can be created easily using [Emacs table mode].
 
 ### Pipe tables
 
+**Extension: `pipe_tables`**
+
 Pipe tables look like this:
 
     | Right | Left | Default | Center |
@@ -1515,7 +1521,7 @@ and lists, and cannot span multiple lines.
 Title block
 -----------
 
-*Extension*.
+**Extension: `pandoc_title_blocks`**
 
 If the file begins with a title block
 
@@ -1595,6 +1601,8 @@ will also have "Version 4.0" in the header.
 Backslash escapes
 -----------------
 
+**Extension: `all_symbols_escapable`**
+
 Except inside a code block or inline code, any punctuation or space
 character preceded by a backslash will be treated literally, even if it
 would normally indicate formatting.  Thus, for example, if one writes