+|@exists@|string|Presence of subproperty|@["properties","exists","my_subproperty"]@|
+|@contains@|string, array of strings|Presence of one or more keys or array elements|@["storage_classes_desired", "contains", ["foo", "bar"]]@ (matches both @["foo", "bar"]@ and @["foo", "bar", "baz"]@)
+(note @[..., "contains", "foo"]@ is also accepted, and is equivalent to @[..., "contains", ["foo"]]@)|
+
+h4(#substringsearchfilter). Filtering using substring search
+
+Resources can also be filtered by searching for a substring in attributes of type @string@, @array of strings@, @text@, and @hash@, which are indexed in the database specifically for search. To use substring search, the filter must:
+
+* Specify @any@ as the attribute
+* Use either the @like@ or @ilike@ operator
+* Have an operand of type @string@ that is wrapped in the SQL pattern match wildcard character @%@
+
+For example, the @["any", "like", "%foo%"]@ filter will return all resources that contain @foo@ in the content of at least one attribute of the previously defined types. This is the recommended way to do keyword and file name search across the entire database. Note that only exact substring matches are returned and results are unranked and returned in the order specified by the @list@ @order@ argument.