The Default Value predetermines which entries are selected when the build form opens. It refers to entries by their display value.

• Several entries: a JSON array of strings, e.g. ["Alpha","Gamma"]
• A single entry: its display value as plain text, e.g. Beta
• No default: leave it empty (or [])

Text is never split on commas: a,b refers to one entry displayed as a,b. A display value that is itself a JSON array of strings must be wrapped in an array, e.g. ["[\"x\"]"].

With Enable Value Validation checked, default values that match no entry are ignored. With it unchecked, they are preselected as free-form entries, submitted as typed.