Represents a field in a form. Every field contains name, content type (perhaps just plaintext), type-specific content, and an optional filename.
Gets the value of this form field as a chunk of bytes. If it is a text field, the value gets encoded as an UTF-8 byte stream.
Gets the value of this form field as a String. If it is a binary field, the value is interpreted as an UTF-8 byte stream.
Gets the value as a String, but only if it is a text or simple field. For binary fields it returns None.