Hence any capabilities with the current Gecko's XML DOM and JavaScript are major bonuses to the MathML engine. This enables to get special effects that would otherwise be impossible. The inline style attribute which is part of MathML 1.0 is missing in the current code. These attributes cannot easily be supported at the frame construction level where MathML frames are created. The formatting presently involved in the MathML code is hooked at the frame construction level.
Every frame is bound to a nsIStyleContext which defines the stylistic characteristics of that frame.
In addition, the Style System enables a frame to possibly hold additional leaf style contexts because they are useful in certain circumstances. Another important task performed by the Style System is dynamic update. If is therefore better to add those style rules that are particular to MathML at the bottom in order to benefit from all this. The Gecko team plans to factor the content code and the frame construction code to allow greater extensibility in these areas. This is something that will certainly benefit the MathML and SVG efforts.