PHP/CodeSniffer/Graze/Sniffs/Naming/AbstractClassNamingSniff.php
public function process(File $phpcsFile, $stackPtr)
    {
        $tokens = $phpcsFile->getTokens();

        if ($tokens[($stackPtr - 2)]['code'] === T_ABSTRACT) {
            $className = $phpcsFile->getDeclarationName($stackPtr);

            if (substr($className, 0, 8) !== 'Abstract') {
                $phpcsFile->addError('Abstract class name "%s" must be prefixed with "Abstract"', $stackPtr, static::ERROR_CODE, '', [$className]);
            }
        }
    }
public function process(File $phpcsFile, $stackPtr)
    {
        $tokens = $phpcsFile->getTokens();

        if ($tokens[($stackPtr - 2)]['code'] === T_ABSTRACT) {
            $className = $phpcsFile->getDeclarationName($stackPtr);

            if (substr($className, 0, 8) !== 'Abstract') {
                $phpcsFile->addError('Abstract class name "%s" must be prefixed with "Abstract"', $stackPtr, static::ERROR_CODE, '', [$className]);
            }
        }
    }
Called when one of the token types that this sniff is listening for
is found.

The stackPtr variable indicates where in the stack the token was found.
A sniff can acquire information this token, along with all the other
tokens within the stack by first acquiring the token stack:

<code>
$tokens = $phpcsFile->getTokens();
echo 'Encountered a '.$tokens[$stackPtr]['type'].' token';
echo 'token information: ';
print_r($tokens[$stackPtr]);
</code>

If the sniff discovers an anomaly in the code, they can raise an error
by calling addError() on the PHP_CodeSniffer_File object, specifying an error
message and the position of the offending token:

<code>
$phpcsFile->addError('Encountered an error', $stackPtr);
</code>

@param File $phpcsFile The PHP_CodeSniffer file where the
token was found.
@param int $stackPtr The position in the PHP_CodeSniffer
file's token stack where the token
was found.

@return void|int Optionally returns a stack pointer. The sniff will not be
called again on the current file until the returned stack
pointer is reached. Return (count($tokens) + 1) to skip
the rest of the file.