The Cas Editor docs say that only XCAS file formats are supported.
This is a bit unfortunate if still true, because that format is not
"preferred" (see the UIMA Docs which say in section 3.2.7 of
tutorial/user guide:
The CASes are stored in an XML format. There are two forms of this
format. The preferred form is the XMI form (see Section 8.3, “Using XMI
CAS Serialization”
<http://incubator.apache.org/uima/downloads/releaseDocs/2.2.1-incubating/docs/html/tutorials_and_users_guides/tutorials_and_users_guides.html#ugr.tug.xmi_emf.using_xmi_cas_serialization>).
An older format is also available, called XCAS.
-Marshall
