If you ever tried to use Perl regular expressions to search for an item in UE, you might have noticed that even
if your regular expression specifically searches using case-sensitive tokens, the results may match words that
do not match on the case-sensitivity.
For example:

If you search for " [A-Z]+\d+ " you would normally expect that you will find words that contain all uppercase letters
followed by at least one digit - like: HOME2, ABD445, etc...
Unfortunately UE interpretation of that regular expression is not compliant with Perl rules, and the search can match
words like: home2, hOMe3, ad77, as well as HOME2, ABD445, etc...

The only way to force any regular expression test in UE to adhere to true REGEX standards is to check the "Match Case" option.

To me this behaviour contradicts what everybody else understands as "Perl regular expressions" but unfortunately UE team
does not want to change this since according to email I got from them: "the thinking was that these two options would conflict with each other".
By the two options they mean the MatchCase option and the true Regex syntax.

The same case-sensitive problem also affects all other places in UE where Perl regular expressions can be used,
for example if Perl regexs are used in wordfiles, they too will ignore the case-sensitivity, and that cannot be explained
by any possible conflict with "MatchCase" option since it does not exist for wordfiles.

Since this has been a decision made by UE team, they will not change it unless enough people will complain.
Personally I believe that since regular expressions are an advanced feature, they should not contain "shortcuts"
to make sure that novices will not get stung.

Please write a letter to UE if you agree with me on this subject.

I disagree.

First, "Perl regex" is a commonly used term that might better be called "Perl style regular expression". It doesn't mean that a native Perl regex can be used in an editor that support Perl regexes (otherwise you'd need to add / around the regex and use mode modifiers like /m etc.). It just means that the basic syntax of the regular expressions follow Perl regex rules. UE and most other editors that support "Perl regexes" don't implement the entire engine (omitting features like Unicode properties \p{Letter} etc.). It's not a patented name.

Second, case-insensitive search is the default in nearly every editor, word processor etc. It would be highly counterintuitive to change that simply because the user has switched from plain text to regex search.

Just my $.02
Tim

I can only add that (1) case sensitivity is a very basic feature of regular expressions that is present in practically all version of them.
And (2) The user who is just switching from plain text to regex search is likely to read about the way they work, and will rather
be surprised by them not working as they should.

On top of that UE help shows examples like:

For example [ abc], will match any of the characters 'a', 'b', or 'c'.
For example [ a-c] will match any single character in the range 'a' to 'c'.

Note that even in UE own help message there is no mention at all that [abc] can also match B.

The feature is there, and there is a checkbox to enable it.

Show me one editor that changes case sensitivity behavior when switching from plain text search to regex search. It would be very bad usability practice to change a setting implicitly when the user selects a different option elsewhere (unless the selected option leaves no other choice, which definitely isn't the case here).

What should UE do? Set a checkmark in the "case sensitivity" checkbox when you select "regular expressions" and clear it again when you select plain text search? What if you had case sensitivity enabled in plain text search, then switch it off during regex search, and then select plain text search again? Should it turn it on again? Leave it off?

A workaround to operate with case sensitive tokens in Perl Regex regardless of the setting of "match case" in UE is to prefix with (?-i) modifier. It means turn off case insensitivity.

Example:

(?-i)[A-Z]+\d+

Read on at Regular-expressions.info / modifiers...

Using Help of UE and typing in boost I was able to get this from the documentation.


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