Alexander The Great 

Could you give me a few examples of what not to find?  I don't really understand what you are trying to achieve here.

Hi Paul 

Paul said:

Could you give me a few examples of what not to find? 

I mean, for example, false search results when the first letter is actually not first in the word

Did I apply the \< incorrectly here:

It is not giving me what I actually expect

Alexander The Great 

ok, I think I see what you're trying to do.  The first point is that the use of \< will just look literally for the < character, so that would be why you don't find anything.  Perhaps you just want word boundaries?  Try this:

\bК\w+\sТ\w+\sП\w+\b

I left out the brackets and the fins space because I don't think they're needed based on your example.

Hi Alexander The Great ,

I think this regex will match 3-letters acronyms:

\b(\w)\w+\s(\w)\w+\s(\w)\w+\s\(\1\2\3\)

Don’t forget to check Regular Expression and Use Backreferences check boxes:

This regex will only find an expanded term with its abbreviation in parentheses. As far as I understand Alexander wants to find all expanded candidate terms using each letter of the abbreviation as the first letter of the candidate words. Adding \b before his regex will do the trick: \b[К]\w+\s[Т]\w+\s[П]\w+\s+
Imagine you have the abbreviation CAT in your text. Task: find terms like crisis action team, computer aided translation, computer assisted teaching, creation and translation, common admission test, etc. for you to guess [or decide based on context] the correct one.

thanks Paul,

this helped and \b works for me.

I believe this option is very useful when need to decide what a certain abbreviation means and how properly expands

and this functionality should be implemented not just by filtering with regex but with a simple filter field

Johnathan Barker said:

Task: find terms like crisis action team, computer aided translation, computer assisted teaching, creation and translation, common admission test, etc. for you to guess [or decide based on context] the correct one.

you guessed just right and the \b[A]\w+\s[B]\w+\s[C]\w+\s+ works great for me. It will help me in future with new abbreviations I am sure 

thanks

Jesús Prieto said:

\b(\w)\w+\s(\w)\w+\s(\w)\w+\s\(\1\2\3\)

definitely interesting regex, not what I was actually looking for but way more advanced. 

Can be used to check if all key abbreviations are expanded at least once

The regex could be refined to reduce false positives (such as "abbreviations" that include digits (such as A1) and complete uppercased terms (such as AB)) and also avoid the false negative at the end of line; the class construction ( such as [A] is not strictly necessary): 

\bA\p{Ll}+\sB\p{Ll}+\sC\p{Ll}+(\s|\b)

The Unicode p{Ll} metacharacter matches lower case letters.

The regex could be refined to reduce false positives (such as "abbreviations" that include digits (such as A1) and complete uppercased terms (such as AB)) and also avoid the false negative at the end of line; the class construction ( such as [A] is not strictly necessary): 

\bA\p{Ll}+\sB\p{Ll}+\sC\p{Ll}+(\s|\b)

The Unicode p{Ll} metacharacter matches lower case letters.