Expr content model is incorrect in dr-flat.rnc

[greenTara]

Expr.content =
  meta-roles.content,
  (element op { op-Expr.type }
   | op-Expr.content),
  element slot { slot.type }*,
  ((arg | arg.content)+ | repo? | repo),
  element slot { slot.type }*,
  resl?

a) does not allow no arguments
b) has a redundant choice: repo? | repo

The correct RNC would be

Expr.content =
  meta-roles.content,
  (element op { op-Expr.type }
   | op-Expr.content)?,
  element slot { slot.type }*,
  ((((arg | arg.content)+ | repo?)|repo),
  element slot { slot.type }*)?,
  resl?

(Note the optional operator as well for keyref instances.)