我想通了 - 使用反向引用。

 （[']）（小于？Q>？+）\1 
 

Question 1:

For example,

     ... "ab'cd" ... 'ab"cd' ...

It should get ab'cd and ab"cd respectively. There may be many quoted strings.

Question 2:

And how to extract text <td>...</td> text from the following string?

<abc>text <td>...</td> text</abc>
<xyz>text <td>...</td> text</xyz>
<def>text <td>...</td> text</def>

abc, def, xyz may be nested in <td>.

I figured it out - using back reference.

(["'])(?<q>.+?)\1