Question

I have a plugin tag [crayon ...] that may or may not be rendered in a <p></p> block like so:

<p>This is a <b>sentence</b> [crayon ...] The Crayon [/crayon] of words. </p>

Since my tag is replaced by a <div> tag, the <p> is left disjoint from </p> and the browser closes it for me, leaving a blank paragraph above my plugin. In any case, the markup is invalid and has weird outcomes. My problem is that I need to detect if [crayon lies between a <p></p> block. I have found two ways so far:

1. Use <p(?:\s+[^>]*)?>(.*?)</p(?:\s+[^>]*)?> and search for [crayon in the capture.
2. Use <p[^>]*>(?:[^<]*<(?!/?p(\s+[^>]*)?>)[^>]+(\s+[^>]*)?>)*[^<]*\[crayon for the case of <p>...[crayon where … doesn’t contain a </p> or <p> and a similar method for a </p> after the [crayon] tag.

The second method is harder to read but will fail if a </p> is captured before my tag. It doesn’t require any further processing to find my tag within the <p></p> like the first. However, the first regex is much simpler and will execute quicker. Which should I use, and is there a better way?

EDIT:

For method 2, this beast works:

<p[^<]*>(?:[^<]*<(?!/?p(\s+[^>]*)?>)[^>]+(\s+[^>]*)?>)*[^<]*((?:\[crayon[^\]]*\].*?\[/crayon\])|(?:\[crayon[^\]]*/\]))(?:[^<]*<(?!/?p(\s+[^>]*)?>)[^>]+(\s+[^>]*)?>)*[^<]*</p[^<]*>

Answer 1

Edit with improved regex, notice I also stole your open p tag detection ;). On PHP, had to add the s modifier for multi line match:

/(?<!<!--)<p[^<]*>(?:[^<]*<(?!/?p(\s+[^>]*)?>)[^>]+(\s+[^>]*)?>)*[^<]*\[crayon.*?\].*?\[\/crayon\].*?<\/p>(?!(\s)?-->)/s

The following string was used for testing. 5 matches expected, 179 steps taken (the single regex from question took 285 steps):

<p>This is a <b>sentence</b> [crayon]...[/crayon] of words.</p>
<p class="large"> Paragraph with parameters [crayon]...[/crayon]</p>
<p>[crayon with-parameters=true]...[/crayon]</p>
<p>
Multiline paragraph [crayon]...[/crayon].
Lorem ipsum.
</p>
<p>...</p><p>[crayon]...[/crayon]</p>
<!-- <p> --> This is a <b>sentence</b> [crayon]...[/crayon] of words.<!-- </p> -->
<pizza>yummy</pizza>

Any improvement?