Standardize coding style in sniff XML documentation code examples

[rodrigoprimo]

As discussed in #1108 (comment), currently, there is no established coding style for code examples in the sniff XML documentation files. This has led to inconsistencies in how code examples are formatted across different XML docs.

I'm not sure what the best approach is, but I do think we should have one.

Some options for consideration:

• As @jrfnl mentioned in Squiz/SelfMemberReference: update XML doc #1108, it could be based on the standard the sniff belongs to, but then what coding standard to use for the Generic sniffs?
• Use the PHPCS coding style.
• Anything else?

[jrfnl]

Use the PHPCS coding style.

Not so sure about that as the PHPCS coding style is quite custom. I think PSR12 might be more appropriate in that case.

Having said that, I agree it would be nice to set some standard, but only if we can also safeguard it - which may be difficult for the "invalid" code samples.

All in all, low priority.