debugging

I'm sure I've forgotten something simple about how to debug templates.

I have DEBUG_ALL on and I'm seeing this message:


keyword-index: Template undef error - id is undefined


keyword-index.tt is a template but it doesn't have any variable or
component of a variable called id


Neither do I see how to connect the error messages with any of the debug
output above it, which is a bunch of lines similar to the last pair:


[Template::Context] filter(lower, [ ]<no alias>)
[Template::Filters] fetch(lower, <no args>,
Template::Context=HASH(0xe614920))


Any thoughts on how to identify my error gratefully received.

Cheers, Dave