Custom tags under MathML

Hi,

I want to used MathML for representing mathematical equations for one of my software products. But I want to specify a custom tag under a MathML tag. How do I do it?

For e.g.

<Apply>
                <Plus/>
                <ci> <get-param Index="1222"  Sub-index="1"/></ci>
                <ci> <get-param Index="1222"  Sub-index="2"/></ci>
</Apply>

Now, there is a parser which knows what is <get-param> accordingly it sets up some configuration at startup. How do I do it?

/Girish