@KevinH:
Some regex search engines actually return 0 length matches and allow you to step through them using "find next".
In cases like that using your string:
Code:
<p> this is a line of text </p>
The first "match" would be a zero-length match ('<')
Hitting Find again would match 'p'.
Hitting Find again would be a zero-length match ('>')
Hitting Find again would be a zero-length match (the space)
Hitting Find one more time would match 'this'
etc...
Sigil's regex search feature has never "advanced" beyond the first zero-length match to my knowledge. And I don't see any compelling reasons to make it do so. Having to hit "Find" two, three (or more) times before you find a "real" match doesn't seem all that useful or intuitive to me.