Sentence:  By a pure error, or perhaps through a confusion in the traditions, Achish the Philistine (of Gath, 1 Sam. xxi., xxvii.), to whom David fled, is called Abimelech in the <WSD>superscription</WSD> to Psalm 34. 
Meaning of the word marked with <WSD> tags:  An editorial addition at the beginning, often indicating the authorship of a piece.