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