(info "(mailutils) Specifying Messages") simpler English

(info "(mailutils) Specifying Messages") says

     Header match
          The "header match" is a string in the form:

               [HEADER:]/STRING/

          It selects all messages that contain header field HEADER matching
          given REGEXP.  If the variable 'regexp' is set, the STRING is
          assumed to be a POSIX regexp.  Otherwise, a header is considered to
          match STRING if the latter constitutes a substring of the former
          (comparison is case-insensitive).

Maybe instead say

     Header match
          The "header match" is a string in the form:

               [HEADER:]/STRING/

          It selects all messages that contain header field HEADER matching
          given **STRING**.  If the variable 'regexp' is set, the STRING is
          assumed to be a POSIX regexp. (All comparison is
          case-insensitive in either case).