These take no input parameters, and output a string. This string is the name of the tag that will be used for this field. Commonly, it is sufficient to use the standard method, Tag, which just returns whatever string is passed to it. You may enforce tag naming standards by writing a tag method that formats a string in a certain way. This method type is not called for each frame, but on demand, so it must return the same value no matter when it is called. Therefore, it doesn't make sense to use inter-frame data, and it has no access to the current frame. The output string must come completely from the parameters passed to it.
Here is the code for the standard method:
TAG
METHOD Tag /* This returns the constant string passed to it */
CODE
csOutput = csParam1;
ENDCODE
PARAM "Constant" Str