How to read a fragment of the C language standard?

Question

C++ / C#

How to read the syntax of C identifiers here?

Answer 1

It's some kind of Backus-Naur notation, I think. View record

X:
    A
    B
    C

Should be read as "X is A or B or C". When two definitions are in a row, it means that they follow each other. Those definitions that are defined in terms of others are non-terminals, those that are self-explanatory are terminals. All this works recursively. In short, this will give you an idea about this https://ru.m.wikipedia.org/wiki/Backus_Form_—_Naura
Well, read it like this: an identifier (identifier) ​​is a sequence of characters that may not be a digit (identifier-nondigit) either start with an identifier (recursion) and continue with a non-digit, or start with an identifier and continue with a digit (digit)
Next comes the deepening - what is identifier-nondigit, what is digit, and so on.

Answer 2

Read more on this,
rfc will come in handy later. ABNF