A class which can parse a normal parameter, or can optionally be filled by some other context.
A class which can parse a normal parameter, or can optionally be filled by some other context.
The type to parse.
The context type which specifies how to parse the value if it's not present.
The parsed value.
Used in Or.
Used in Or. Parse a value, or return the sender as that value. Requires that a UserValidator is present for that type.