Add a small documentation for hiliteMatches

src/libutil/fmt.hh

@@ -156,5 +156,12 @@ inline hintformat hintfmt(std::string plain_string)
     return hintfmt("%s", normaltxt(plain_string));
 }
 
+/**
+ * Highlight all the given matches in the given string `s` by wrapping them
+ * between `prefix` and `postfix`.
+ *
+ * If some matches overlap, then their union will be wrapped rather than the
+ * individual matches.
+ */
 std::string hiliteMatches(const std::string &s, std::vector<std::smatch> matches, std::string prefix, std::string postfix);
 }