php regex to match outside of html tags

Question

I am making a preg_replace on html page. My pattern is aimed to add surrounding tag to some words in html. However, sometimes my regular expression modifies html tags. For example, when I try to replace this text:

<a href="example.com" alt="yasar home page">yasar</a>

So that yasar reads <span class="selected-word">yasar</span> , my regular expression also replaces yasar in alt attribute of anchor tag. Current preg_replace() I am using looks like this:

preg_replace("/(asf|gfd|oyws)/", '<span class=something>${1}</span>',$target);

How can I make a regular expression, so that it doesn't match anything inside a html tag?

Answer 1

You can use an assertion for that, as you just have to ensure that the searched words occur somewhen after an >, or before any <. The latter test is easier to accomplish as lookahead assertions can be variable length:

/(asf|foo|barr)(?=[^>]*(<|$))/

See also http://www.regular-expressions.info/lookaround.html for a nice explanation of that assertion syntax.