// must at the least provide:
//
//	func (n *MyNode) String() string { return fmt.Sprint(n) }
//	func (n *MyNode) rawCopy() Node { c := *n; return &c }
//	func (n *MyNode) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
//
// The embedding struct should also fill in n.op in its constructor,
// for more useful panic messages when invalid methods are called,
// instead of implementing Op itself.
type miniNode struct {

		valid := true
		switch mode := finfo.flags & fMode; mode {
		case 0:
			finfo.flags |= fElement
		case fAttr, fCDATA, fCharData, fInnerXML, fComment, fAny, fAny | fAttr:
			if f.Name == xmlName || tag != "" && mode != fAttr {
				valid = false
			}
		default:
			// This will also catch multiple modes in a single field.
			valid = false
		}
		if finfo.flags&fMode == fAny {
			finfo.flags |= fElement
		}