Standards are specified by classes that implement the PHP_CodeSniffer_Sniff
interface. A sniff registers what token types it wishes to listen for, then
PHP_CodeSniffer encounters that token, the sniff is invoked and passed
information about where the token was found in the stack, and the token stack
itself.
Sniff files and their containing class must be prefixed with Sniff, and
have an extension of .php.
Multiple PHP_CodeSniffer operations can be performed by re-calling the
process function with different parameters.