[howto] add a filter to getElementsBy<whatever>

hi,

I want to write a function to filter the result of getElementsBy<whatever> to be able to write lines such as:

var result=getElementsByTagName("tr").filterfunc(<some params>)

I think getElementsBy... return an array. in what prototype should I plug the filterFunc to be able to write such an instruction ? BTW, in this function, will the array be availble under 'this' ?

TIA,
Pierre.