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Can someone explain this regexp command?

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Justin Schrout
Justin Schrout 2017-5-16
编辑： Stephen23 2017-5-17
I have some code:
expr = '<Placemark>.*?</Placemark>';
objectStrings = regexp(txt,expr,'match');
This works exactly as I would like it to. However, I am not fundamentally understanding what Matlab is doing, specifically when I see the .*? I have pored over the documentation, but I am just not understanding. Would someone please be kind enough to explain what is happening?

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Stephen23
Stephen23 2017-5-17
编辑：Stephen23 2017-5-17
It is quite simple:
<Placemark> % match literal string
.* % match any characters, any number of times
? % makes the previous quantifier lazy (ie *)
</Placemark> % match literal string
The MATLAB documentation explains how regular expressions work:
https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html
And we find it explains all of those parts of your regular expression:
  • angle brackets are not special characters, therefore the "placemark" parts are interpreted literally.
  • " expr* 0 or more times consecutively."
  • " exprq? Lazy expression: match as few characters as necessary."

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