[exim] Exim Conditions

Hi,
Is there anyone how can describe creating of ACL's conditions ? Wiki doesn't said enough about this. For example:
1. condition = ${if >{$demime_errorlevel}{2}{1}{0}} - why there is 3 kind of value (2,1,0) ?
2. condition = ${lookup{$authenticated_id}lsearch{/etc/mail/block_accounts}{yes}{no}} - why there is yes and no ?
3. and many other

On net theres thousands of examples with multiple value after variables but how use them ?

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Pozdrawiam / Best Regards
Michał Giżyński
http://nat.net.pl