The bottom panel of Figure lists some major notable features of the standard. Certain CV terms from a list that accompanies the specification or the Unimod CV for protein modifications may be specified in square brackets. An analyte number may be specified before each annotation (e.g. '1@' or '2@') for cases where more than one analyte may be present in the spectrum ('0@' indicates an unspecified contaminant ion). Such contaminant ions may take a few different forms, such as '0@y2{TK}' to indicate a y2 type ion from some unspecified ion (ending with TK on the C terminus), or '0@_{Adenine}' to indicate a fragment ion corresponding to a nucleotide fragment perhaps from an RNA molecule that entered the selection window (common in phospho-enriched datasets). If multiple peaks gather the same annotation since they are closer together than the annotation m/z tolerance, the less likely duplicates may be enclosed in square brackets.