How to convert a .Net regular expression to php -

i have regular expression used replace phrase if phrase not contained html anchor tags or img tag. example phrase being searched "hello world"

the .net regular expression

(?<!<a [^<]+)(?<!<img [^<]+)(?<=[ ,.;!]+)hello world(?=[ ,.;&!]+)(?!!.*</a>)

e.g. regular expression should match "hello world" in phrase

"one 2 3 hello world 4 five"

but shouldn't match hello world in phrase like

"one 2 3 <a href='index.html'> hello world </a> 4 five"

"one 2 3 <img alt='hello world' \>four five"

any guidance on how go converting php regex appreciated.

note: not use regular expression parse tags.

for a or img tags specifically, following.

(?!<(?:a|img)[^>]*?>)\bhello world\b(?![^<]*?(?:</a>|>))

i suppose in or between tags, try this.

(?!<[^>]*?>)\bhello world\b(?![^<]*?(?:</[^/]*>|>))

Bradly