Circumflex and dollar
Square brackets
PCRE regex syntax
PHP Manual

## Full stop

Outside a character class, a dot in the pattern matches any one character in the subject, including a non-printing character, but not (by default) newline. If the PCRE_DOTALL option is set, then dots match newlines as well. The handling of dot is entirely independent of the handling of circumflex and dollar, the only relationship being that they both involve newline characters. Dot has no special meaning in a character class.

\C can be used to match single byte. It makes sense in UTF-8 mode where full stop matches the whole character which can consist of multiple bytes.

Circumflex and dollar
Square brackets
PCRE regex syntax
PHP Manual