tableNumberProblem function
Why raw, trimmed, is not a table number, or null when it is one (T4):
non-empty, at most kTableNumberMaxLength code units, no control
character (no line break).
Implementation
TableNumberProblem? tableNumberProblem(String raw) {
final n = raw.trim();
if (n.isEmpty || n.length > kTableNumberMaxLength) {
return TableNumberProblem.length;
}
if (n.codeUnits.any(isControlCodeUnit)) return TableNumberProblem.control;
return null;
}