The ST02 element is defined by the X12 Standard as an alphanumeric (AN) value. The 'AN' element is a sequence of characters from the basic or extended character sets, which includes numeric values or numbers. The 005010X212 (276/277) TR3 ST02 element name is Transaction Set Control Number, and the element note states: The Transaction Set Control Numbers in ST02 and SE02 must be identical. The number is assigned by the originator and must be unique within a functional group (GS-GE). For example, start with the number 0001 and increment from there. The note states 'The number' (i.e. numeric value) as opposed to 'The value' (which could be numeric, alphabetic or special characters) and also provides a numeric example for creating uniqueness. Therefore the intent of the 5010 276/277 TR3 element note, establishes the ST02 as only allowing a number or numeric value that must be unique within the group and interchange.