For now, you'll have to refer to the example filters as found in the current report specification files. We'll give one other example here: specifying a time range.
Suppose you want to be able to report on only a specific time range. You could build a (possibly global and reused) filter like:
<lire:filter-spec> <lire:and> <lire:ge arg1="$timestamp" arg2="$period-start"/> <lire:le arg1="$period-end" arg2="$timestamp"/> </lire:and> </lire:filter-spec>
When trying your new filter, you could install it in ~/.lire/filters/your-filter-name.xml. When lr_dlf2xml looks up a filter which was mentioned in the report configuration file, it looks first in ~/.lire/filters/, and then in .../share/lire/filters/.