pagereference – Labels and references in Plain TeX

Pro­vides a mech­a­nism for record­ing the lo­ca­tion of la­bels placed in a doc­u­ment. The pack­age re­quires a two-pass pro­cess (it asks the user whether this is the “sec­ond pass”). The first pass es­tab­lishes where things are (writ­ing the val­ues of page la­bels to a .pgn file), the sec­ond pass fills in the ref­er­ences.
There is no equiv­a­lent of the LaTeX mech­a­nism for check­ing whether la­bels have changed dur­ing a run.