Same above.  The two arguments here could be any type really.

And this follows FE 1 & 2 where PropertyIsEqualTo takes two expressions.  See XSD or the FE examples (e.g. from Page 32 of 1.0):
```xml
<PropertyIsEqualTo>
  <PropertyName>PROPA</PropertyName>
    <Add>
        <PropertyName>PROPB</PropertyName>
        <Literal>100</Literal>
    </Add>
</PropertyIsEqualTo>
```

In ol3, you'd get the same when parsing `PROPA == PROPB + 100`.