name: editor1
symbols: input_box, palette, palette_row, palette_tab, palette_whitespace

input_box: a symbol that is a placeholder (usually shown as a box) which
  indicates that a subformula could be entered here.

palette: an n-ary function indicating a palette for an input editor. It has as
  arguments either only palette_tabs or only palette_rows. If palette_rows are
  used as arguments, then they should have the same length.

palette_row: an n-ary function describing the entries of a row in a palette for
  an input editor. 

palette_tab: an n-ary function describing a tab in a palette. The entries
  should be palette_rows with the same number of arguments. [unused]

palette_whitespace: a symbol indicating that there should be a placeholder in
  the palette, that can not be used to input anything.

other palette items:
- using images or mathml to display the symbols (use a service once)
- 'custom presentation' (mathml-like)
- maximum size ?
- function