A regular expression and a Windows permission (cacls) question

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Hello, firstly, what does the regular expression "\\+" do? Would that literally match up "\+". Could I possibly get some recommendations on some software to try regular expressions with as well actually please?

and secondly, i've been fiddling around with the cacls command and ive noticed that it doesn't seem to be able to give users "modify" access. It can

give read, write, change and full control to users but not modify (and I think some others too). How do you grant modify access to a file in the command line?

(this is for my coursework and i'm kind of stumped on these two questions).

Thanks guys.