[chaley]

@capink: what do you think about a template function

is_book_var_defined('var_name')

that returns '1' or ''.

The function would get around the ambiguity between a defined book_var that contains '' and an undefined book_var. Something like this:

	if is_book_var_defined('foo') then
		result = book_vars('foo')
	else
		result = field('whatever')
	fi;
	result