Content models differ syntactically but not (?) semantically

I wish to have the difference between the following two content models
clarified.

Taken from the table-section headed
'When the <complexContent> alternative is chosen, the following elements
are relevant ...'
in the table entitled
'XML Representation Summary: complexType Element Information Item'
in section 3.4.2 'XML Representation of Complex Type Definitions:'

<restriction
 base = QName
 id = ID
 {any attributes with non-schema namespace . . .}>
 Content: (annotation?, (group | all | choice | sequence)?, ((attribute
| attributeGroup)*, anyAttribute?))
</restriction>

<extension
 base = QName
 id = ID
 {any attributes with non-schema namespace . . .}>
 Content: (annotation?, ((group | all | choice | sequence)?, ((attribute
| attributeGroup)*, anyAttribute?)))
</extension>

Thank you,
Mark Ingram.