Expose multi-select dropdown “chip” data validation via sheet API

[mathieu-tracklab]

Description:

• What I need: Programmatic control to create & edit Data Validation rules that (a) use “Dropdown (chip)” display and (b) enable Allow multiple selections; plus the ability to read whether a rule is chip vs arrow and whether multi-select is on.

• Why: I auto-generate template Sheets in Python. Today I must pre-bake rules in a manual template; if I ever clear/edit validation, multi-select/chip can’t be re-created programmatically.

• API/Fields requested: New fields in Sheets API v4 DataValidationRule (e.g., displayType: CHIP|ARROW, allowMultiple: true|false).

• Impact: Blocks reliable automation for enterprise templates; requires fragile manual steps.

I'm at disposal if the request is unclear.