This PR is a replacement for the original PR #132736 that I have accidentally ruined. 😬

Related Issue: #150626

Original PR description.

Hello, let me try to help a bit with docs.

Here is an string formatting example:

In [29]: "{a-b} {-}".format(**{"-": "_-_", "a-b": "ABC"})
Out[29]: 'ABC _-_'

This behaviour differs from Format String Syntax:

arg_name: [identifier | digit+]
attribute_name: identifier

So I updated arg_name and attribute_name syntax in that section to follow the actual behaviour:

• replaced identifier with attribute_name in arg_name
• set syntax for attribute_name as anything that doesn’t contain "." or "]"

You can find original discussion thread here

• Issue: Clarify that format strings accept arbitrary tokens as field names #150626