Except for the capture group syntax, other (?...) The syntax is not the verification of the capture group.

Except for the capture group syntax, other (?...) The syntax is not the verification of the capture group.

See the following content in a regular expression technical document:

"It must be noted that apart from (Expression) and (? <Name> Expression) syntax, other (?...) Neither of the syntax is a capture group ."
This content is understandable, but I am confused that the author of this article, in another technical article on related regular expressions, is an example of this, which really puzzles me:

Text Content

<td>a</td><td>b</td> 

Regular Expression

(?is)<td>(?:(?!</td>).)*</td> 

Pay attention to the code of the regular expression above. </Td>). "force a non-capturing group. I told him in the text message that it could be written as follows :(? Is) <td> ((?! </Td>).) * </td>
Two days later, I still didn't see him reply, so I looked back at his code. At first I focused on "(?! </Td>) "This bracket is not a capture group. However, I only reflected the code in the above technical article once. He is not targeting (?! </Td>) force (?! </Td>). The force is not a capture group, so I did the following test:

Text Content

<td>a</td><td>a</td>

Regular Expression

<td>((?!</td>).)*</td><td>(\1)*</td>

Matching result

<td>a</td><td>a</td>

This proves that, if not, "(?! </Td>). "to force a non-capturing group, it will be captured, and I don't need it at all.
Next, I'm testing, except (Expression) and (? <Name> Expression) except the syntax, for example, loop view, it is not a capture group.

Text Content

<td>a</td><td>a</td> 

Regular Expression

<td>((?!</td>).)*</td><td>(\2.)*</td>

Matching result: Mismatch
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