- merge space and space list attribute.
- may be merge space and lentgh attribute (for example by extending GMATHML_UNIT with the different GMATHML_NAMED_SPACE).
- check memory allocation in gmathmlattributes.
- also check array access in update/measure/layout/render methods.
- need_layout flag (extend attribute to mark them as layout invalidator (FALSE for color attribute, for example)).
- stretching support (done for under/over).
- mtr/mtd attribute support.
- get_embellished_core for mmultiscripts, semantics, maction, mrow (and infered rows) (Mathml 2.0 3.2.5.7.3)
- is_inferred_row for merror, mpadded, menclose,
- build a view tree for data specific to a given view.
- handle correctly PT and PX units.
- handle table alignment. Correctly compute axis position in a row.
- merge attribute code in presentation_token and style_element.

And many many more things to do...
