Provided by module: Tags: RXML tags
Does the given variable exist? I.e. is it bound to any value, be it null or something else?
The difference from the <if variable> plugin is that this one returns true for variables with a null value (typically produced by the <emit source="sql"> for columns containing an SQL NULL value).
Compatibility note: When the compatibility level is 4.5 or lower, <emit source="sql"> assigns the undefined value for SQL NULLs instead of a proper null value. This test is therefore false for such values too unless the compatibility level is higher than 4.5.