Not-regular expressions & derivatives
http://www.dcc.fc.up.pt/dcc/Pubs/TReports/TR13/dcc-2013-11.pdf

http://www.home.hs-karlsruhe.de/~suma0002/publications/cc14-flexible-lexing-via-extended-regex.pdf

Regular Path Queries & regular expressions

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Russ Cox

   https://swtch.com/~rsc/regexp/regexp1.html
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about extended regular expressions
  http://www.ddfy.de/
  http://perl.plover.com/NPC/


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https://books.google.co.uk/books?id=Z3qkDAAAQBAJ&pg=PT492&lpg=PT492&dq=%22improve+security%22+%22regular+expressions%22&source=bl&ots=RlTKL1pKe-&sig=CJ-DNODICsUx_8OfuRzlcDDTKH4&hl=en&sa=X&ved=0ahUKEwidlaXA58zRAhWBAsAKHfIXCj0Q6AEIODAF#v=onepage&q=%22improve%20security%22%20%22regular%20expressions%22&f=false



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Regexes and automata

http://link.springer.com/article/10.1007/s11265-015-1052-y
http://ieeexplore.ieee.org/abstract/document/7468531/
http://www.arl.wustl.edu/~pcrowley/
http://regex.wustl.edu/index.php/Regular_Expression_Processor



Contextfree expressions
https://arxiv.org/pdf/1610.06832.pdf