base type of token , normalizedString ?? why ?

[Rahul]

I dont' understand why the base type of token as defined in the xml
schema definition is "normalizedString" instead of "string" .

<simpleType name="token">
<restriction base="normalizedString">
<whiteSpace value = "collapse" />
</restriction>
</simpleType>


<simpleType name="normalizedString">
<restriction base="string">
<whiteSpace value = "replace" />
</restriction>
</simpleType>


to me it seems that the definition of 'token' could have been

<simpleType name="token">
<restriction base="string">
<whiteSpace value = "collapse" />
</restriction>
</simpleType>

why was it not defined this way instead ??? what am i missing ??