Extract a specific property from each item in a list.

This filter extracts a named property from maps, proplists, or resources in a list, returning a new list containing only those values.

For example:

    {{ items | extract:"price" }}

When items is a list like [#{price => 10, name => "A"}, #{price => 20, name => "B"}], this returns[10, 20]. This is particularly useful when combined with the sum filter for analytics: ```django {{ orders | extract:"amount" | sum }} ``` When extracting from resources, you can use any valid resource property: ```django {{ m.search[{query cat="product"}] | extract:"title" }} ``` If applied to a single item instead of a list, it extracts and returns the property value from that item. If the input isundefined, the filter returns an empty list[]`.