[Standards] XEP-50: Schema and text contradiction regarding 'note' element

[Florian Schmaus]

XEP-50 § 4.3 states about the note's element 'type' attribute:

This attribute is OPTIONAL, and implies "info" if not present.

while the Schema in § 8 makes the 'type' attribute required:

  <xs:element name='note'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='type' use='required'>


For me as library developer, it's easier to implement the non-optional
case that the schema describes, as it doesn't require an extra case if
the attribute is missing.

Pointed out in https://community.igniterealtime.org/thread/53776

- Florian