The value bound to a placeholder when formatting a message.

• Str — for {name} and select arguments.
• Int / Float — for number, plural, and selectordinal arguments.
• Time — for date and time arguments.

A best-effort plain-string rendering, used when a value is substituted for a bare {name} placeholder (no type/format). Numbers are rendered without locale formatting; use a number placeholder for that. Times render as their epoch milliseconds, which is rarely what you want — prefer a date/time placeholder.