[Suggestion] create updateAttr method on XMLElement

[GeekTree0101]

I needs update attribute value on XMLElement,
If you don't mind, Please check it
Thank you

[cezheng]

I have thought about supporting modifying XML before, but this will require a major rewrite since the current implementation heavily relies on lazy.

For this PR, the attributes property will be broken.

[GeekTree0101]

Okey I got it, thanks for code review :)