Possible Bug using Regex in Notepad++ with Replace All? - regex

Question

Have I found a bug in Notepad++ or am I doing something wrong?
Background info
(Please note that I do know that one are supposed not to use Regex parsing HTML, but I think this is a special case that should work - without the possible Notepad++ bug ;-)
I have exported Apple Notes as HTML using Exporter 3.0 on a Mac. In the HTML output every Note line is between <div> - </div> elements and also "header/title lines" like <h1> - </h1> or <h2> - </h2> etc. Each "header/title line" is often split in several unnecessary HTML header elements as in the following simplified example.
<div><h1>TEST </h1><h1>Title<br></h1></div>
<div><b><h2>T1</h2><u><h2>T2</h2></u><h2> </h2></b><h2>(</h2><h2>T3</h2><u><h2>T4</h2></u><h2>)</h2><b><h2><br></h2></b></div>
This HTML can't be imported into OneNote giving the same result as seen in Apple Notes i.e. each "header/title" line is split in multiple lines. That's true even when changing the <h1>/<h2> block elements to inline elements using an initial <style>h1, h2 {display: inline;}</style> statement. (Maybe that is a bug or restriction in OneNote, but I need to find a workaround.)
Therefore, I need to clean the example HTML output above from the unnecessary HTML header <h1> or <h2> (all but the first in every line) and </h1> or </h2> (all but the last in every line), to get the following result that can be imported to OneNote without problem.
<div><h1>TEST Title<br></h1></div>
<div><b><h2>T1<u>T2</u> </b>(T3<u>T4</u>)<b><br></h2></b></div>
Solution ? - Developed Regex
I'm quite new to Regex, especially advanced Regex, but I think I have found a way to clean the erroneous HTML code using TWO different Regex expressions as follows.
Both works well when tested using regex101.com, I think.
The first one is used to remove unnecessary </h1> or </h2> elements and is a Positive Lookahead function (it works both in regex101 and in Notepad++)
(</h[1-6]>)(?=.*?\1)
(Demo)
Picture 1 shows a working Find All + Mark All in Notepad++
Picture 2 shows a working Replace All
The Second one used to remove unnecessary <h1> or <h2> elements and is a Positive Lookbehind function (it works in regex101 but NOT fully in Notepad++)
(?<=(<(h[1-6])>))(?:.*?)\K\1
(Demo)
Picture 3 shows a working Find All + Mark All in Notepad++ = All 8 occurrences found
Picture 4 shows a NOT working Replace All in Notepad++ = Only 5 occurrences (of the 8 found) are replaced
If I redo the same Replace All a second time 2 of the
remaining 3 occurrences are replaced.
If I redo the same Replace All a third time the last
remaining occurrence is replaced.
BUG ?
Is this a bug in Notepad++ or is this behavior normal or am I doing something strange here? Please help me understand.

Answer 1

So, rather than make multiple passes through your data, you can get it all in one pass with this:
(^.*?<h[1-6]>)?(.*?)</?h[1-6]>(?=.*</h[1-6]>.*?$)
and replace it with \1\2. The first capture group skips the first <h#> on each line and is null after line start. The second capture group captures everything up to the next <h#> tag. The optional slash (/?) scans and deletes both open and close tags. The last part is a positive lookahead to make sure the last </h#> is not deleted.
In the two lines of your examples all the header levels were the same on the line and this regex is fine. If the first open and last close don't match, then you have a problem but I think your solutions also have that same problem. In any case you can fix that in a second pass with ^(.*<h)([1-6])(.*<h)[1-6] and replace it with \1\2\3\2.
I would also point out that this creates unbalanced HTML with a <b>, followed by <h1>, followed by </b>, followed by </h1>. I don't know if that is OK for your case. If not, it might be better to remove ALL the <h#> tags and anchor new ones just inside the <div> </div> pair.
In any event here is a REGEX101 screenprint with this regex working on your examples: