$re = '/\{word\}(*SKIP)(*F)|word/m';
$str = 'before a comma word,
end of sentence word.
end of line word
word at line start
prefix-word pattern
and word-postfix pattern
but not {word} as a tag
neither {word} nor
{word} here
word
{word}
{word should match
this should match too word}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php