The Edit Equivalence String... menu item brings up a dialog box indicating
    that an equivalence string is being set.

    Enter a string into the Equivalence String field and
    click on either of the Append or Add Before Selected buttons
    to add the string in the appropriate place in the Equivalence String
    List field. The Equivalence String List field contains a list of
    equivalence strings, one string per line.

    If equivalence information exists for the current context,
    that information is shown in the Equivalence String List field when the
    dialog box is managed. Delete items from the string list by
    selecting the appropriate item(s) in the Equivalence String List field and
    clicking on the Delete Selected button. The OK button accepts the
    string list and dismisses the dialog box. The Cancel button
    dismisses the dialog box without changing the equivalence string.

    Click on the Select... button to specify the string.