Sphinx 3 disallows having more than one productionlist markup with
the same name. Simply remove names in this case, since names are not
shown anyway. For example, fix the Sphinx 3 warning:
Doc/reference/introduction.rst:96: duplicate token description
of *:name, other instance in reference/expressions
The general form of a *standard format specifier* is:
-.. productionlist:: sf
+.. productionlist::
format_spec: [[`fill`]`align`][`sign`][#][0][`width`][`grouping_option`][.`precision`][`type`]
fill: <any character>
align: "<" | ">" | "=" | "^"
The descriptions of lexical analysis and syntax use a modified BNF grammar
notation. This uses the following style of definition:
-.. productionlist:: *
+.. productionlist::
name: `lc_letter` (`lc_letter` | "_")*
lc_letter: "a"..."z"