Add a note to the style guide about abbreviations

documentation/markup.rst

@@ -703,8 +703,14 @@ In the CPython documentation, there are a couple common cases
 where simpler markup should be used:
 
 * ``*arg*`` (rendered as *arg*) for function and method arguments.
+
 * ````True````/````False````/````None```` for ``True``/``False``/``None``.
 
+* ``Full Spelling (abbreviation)`` for abbreviations and acronyms.
+
+  The ``:abbr:`` role generates HTML which is not accessible to some forms of
+  assistive technology and mobile users.
+
 In addition, the CPython documentation defines a few custom roles:
 
 * ``:gh:`ID```: link to a GitHub issue.

documentation/style-guide.rst

@@ -125,6 +125,10 @@ be native English speakers.
 Don't use Latin abbreviations like "e.g." or "i.e." where English words will do,
 such as "for example" or "that is."
 
+The first time an acronym is used on a page, spell it out.
+Prefer to write out the full term and follow it with the acronym in parentheses.
+For example, write "JavaScript Object Notation (JSON)".
+
 
 Charged terminology to avoid
 ============================