For Recoll versions 1.18 and later, and when working with a raw index (not the default), searches can be made sensitive to character case and diacritics. How this happens is controlled by configuration variables and what search data is entered.
The general default is that searches are insensitive to case
      and diacritics. An entry of resume will match any
      of Resume, RESUME,
      résumé, Résumé etc.
Two configuration variables can automate switching on sensitivity:
If this is set, search
              sensitivity to diacritics will be turned on as soon as an
              accented character exists in a search term. When the variable
              is set to true, resume will start a
              diacritics-unsensitive search, but résumé
              will be matched exactly. The default value is
              false.
If this is set, search
              sensitivity to character case will be turned on as soon as an
              upper-case character exists in a search term except
              for the first one. When the variable is set to
              true, us or Us will
              start a diacritics-unsensitive search, but
              US will be matched exactly. The default
              value is true (contrary to
              autodiacsens).
As in the past, capitalizing the first letter of a word will turn off its stem expansion and have no effect on case-sensitivity.
You can also explicitely activate case and diacritics
      sensitivity by using modifiers with the query
      language. C will make the term case-sensitive, and
      D will make it
      diacritics-sensitive. Examples:
        "us"C
   will search for the term us exactly
      (Us will not be a match).
        "resume"D
      will search for the term resume exactly
      (résumé will not be a match).
When either case or diacritics sensitivity is activated, stem expansion is turned off. Having both does not make much sense.