Understand metacharacters and escape character

In most languages, the [escape character](https://en.wikipedia.org/wiki/Escape_character) is '\\'. Sequences start with an escape character have special meaning, eg: '\n', '\t'.

[Metacharacters ](https://en.wikipedia.org/wiki/Metacharacter)are escape characters, but often match a group of characters, eg: '\s' matches any whitespace like '\t', '\n'.

So, when we are matching single comment lines in C, we need to use:

``\/\/[^\n]*``,

instead of

``\/\/[^\\n]*``

which won't match a line break but a "\n" string.

No file or test is named in the issue. Review the repository's existing explanation or examples of C regular-expression patterns, then determine whether the escape-character distinction should be documented or corrected; done means the explanation clearly distinguishes a newline from the literal "\\n" sequence.

Written by the indexing model from the issue text.