code: public boolean replaceIn(final StrBuilder source) {
          if (source == null) {
              return false;
          }
          return substitute(source, 0, source.length());
      }
docs: Replaces all the occurrences of variables within the given source
  builder with their matching values from the resolver.
  
  @param source  the builder to replace in, updated, null returns zero
  @return true if altered