how to: Conditionally call nested XSLs based on parameters or variables

How to Conditionally call nested XSLs based on parameters or variables
passed to it at a higher level?

<stylesheet>

<template chapter>
....
..etc. etc..

        <apply-temp section>
...
..
</>

<temp section>

variables <!-- these are the variables/parameters I want to use for
condns
parameters <!-- QUESTION: what would be the scope of the vars n pars
....            <! -- HOW DEEP would their values go ? For Params I know
only as                 <! -- far as they are pushed down.. what about
Vars ? 
                <! -- will the variables defined at section level be
available
                <!-- to template levels applied to below ??
.....
...<appl-temp toallchildren>
(with or/without params)
...
..
</>

<temp para>

...
..
<appl-temp morediffchildren>
...

</>

BASICALLY: I want to define Variables/Parameters within a section and
ONLY for a section and ALL its CHILDREN below it. 
I do not want these variables to become global as I will be using the
"same" name (is that even possible) variables for OTHER sections.

I want to make the scope of the variables/params available AT section
level and BELOW !!!

Please do let me know.

Thanks,

Abhishek Sanwal

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