es means ees???

[Richard Shann]

In the lilypond 2.19 installed file

usr/share/lilypond/current/ly/chord-modifiers-init.ly

I see the following at line 27

  <c es ges>-\markup { \super "o" } % should be $\circ$ ?


Here, instead of ees, is written es.

I've tried this out, and it appears to be a synonym, but I don't see
this documented. Anyone know what's going on?

Richard