>   not(string(.))	string-length(.)=0
>   not(x)		count(x)=0
>   not(x=y)	        x!=y
> 
> 
>   I always use the expressions in the second column for maintainability,

I usually find the first forms are clearer not(@id) seems to say "no id
attribute" clearer than count(@id)=0. But beware while the first two
pairs are equivalent, not(x=y) is not the same thing as x!=y and I find
it's really dangerous to use != as usually I want not (  = ).
If either x or y is a node set containing nodes with different values
then  x!=y is always true.

David


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