Hi,
The following fragment is valid in XLIFF 2.0:
<unit id="1">
<segment>
<source>text <sc id="A" isolated="yes" fs:fs="i" /></source>
</segment>
</unit>
<unit id="2">
<segment>
<source>other text <sc id="A" isolated="yes" fs:fs="b" /></source>
</segment>
</unit>
Note that both <sc> elements have the same "id". If you want to pair an isolated <ec> with one of those <sc> elements using the "startRef" attribute, you can't differentiate them.
It seems that the "id" attribute of an isolated <sc> element must be unique within the enclosing <file>, but current specification doesn't require that.
Regards,
Rodolfo