Vim XMLns context awareness

I've used Vim's g:xmldata_ to describe XML possible elements to be able to use omni-compete for XML. The problem is not each A node has a0, a1, an. S开发者_JAVA技巧ometimes A node has only a0. And the documentation of the a0 and A is different and depends on parent of A.

E
|
|--A
|  \-a0     // documentation of E.A.a0
|  \-a1
|
\--B
   \-A
     \-a0     // documentation of E.B.A.a0

Documentations of A and a0 are different. But user will see the same help-text in the complete preview window.

Here is the test xmldata to play with. Put this

let g:xmldata_test = {
\ 'vimxmlroot': ['E'],
\ 'E': [['A', 'B']],
\ 'B': [['A']],
\ 'A': [['a0', 'a1']],
\ 'vimxmltaginfo': {
\ 'a0': ['', 'documentation that only confuses an user'] }}

in autoload/xml/test.vim

And execute while edit some xml document

:XMLns test 

To bring up the complete window just type < and press C-X C-O

Is there any way to tell Vim for which a0 I want to set help information?