pub fn requiredness(expr: &ConditionExpr) -> Option<ConditionExpr>Expand description
What of expr decides whether something missing must be sent.
Notes ([500]–[899]) and formats ([900]–[999]) describe a value that
is there, so a missing value cannot fail them, and they say nothing about
whether one is needed. A [UB…] the status could not expand (read as
[0]) is one of the AHB’s date-format unions — UB1: ([931] ∧ [932] [490]) ⊻ ([931] ∧ [933] [491]), whose [490]/[491] ask about the date
itself. All of them are dropped: X ([10]) ∧ ([UB1]) requires its value
where [10] holds, X [914] ∧ [937] always. Read as True instead, the
two sides of UB1’s ⊻ would cancel out.
None when nothing is left: the status’s keyword alone decides.