code: public boolean replaceIn(final StringBuffer source, final int offset, final int length) {
          if (source == null) {
              return false;
          }
          final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
          if (substitute(buf, 0, length) == false) {
              return false;
          }
          source.replace(offset, offset + length, buf.toString());
          return true;
      }
docs: Replaces all the occurrences of variables within the given source buffer
  with their matching values from the resolver.
  The buffer is updated with the result.
  <p>
  Only the specified portion of the buffer will be processed.
  The rest of the buffer is not processed, but it is not deleted.
  
  @param source  the buffer to replace in, updated, null returns zero
  @param offset  the start offset within the array, must be valid
  @param length  the length within the buffer to be processed, must be valid
  @return true if altered