Validation of custom unit and annotation references should allow for automated whitespace normalization

[servilla]

Custom unit and annotation reference validation should allow for automated whitespace normalization to ensure that string values are mapped accurately. This is only a local standard and not part of the XML specification. Therefore, validation testing of normalized strings should be optional.

For example:

...
<customUnit>myUnit   X <customUnit>
...
<stmm:unit id="myUnit   X ">

would be normalized to

...
<customUnit>myUnit X<customUnit>
...
<stmm:unit id="myUnit X">