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+# mkvalidator warning WRN00C "unknown element"
+
+## The problem
+
+When running mkvalidator on a file generated by mkvmerge 5.9.0 or later it issues the following warning:
+
+```
+WRN00C: Unknown element in CueTrackPositions [F0] at 20090944 (size 2 total 4)
+```
+
+What does it mean?
+
+## The answer
+
+mkvalidator has encountered an element that it doesn't know about. This unknown element has the ID `0xF0` and is located as a child element of the well-known element `CueTrackPositions` at byte position `20090944`. The size of its data portion (its "content", so to speak) is 2 bytes, while its total size (EBML ID + length field + data portion) is 4 bytes.
+
+This can happen if mkvdalitor is run against a file that has been created with a mkvmerge version that already uses newer elements from the Matroska specs and mkvalidator has not been updated to match those specs yet. This is the case for the unknown element `0xF0` inside `CueTrackPositions`: looking at [the Matroska specs](http://www.matroska.org/technical/specs/index.html) we can see that `0xF0` is the new element `CueRelativePosition`. The same warning can be seen for the other new element `0xB2` which is `CueDuration`.
+
+**Update 2012-12-16**: A new version of mkvalidator, 0.4.2, [has been released](http://www.matroska.org/downloads/mkvalidator.html) which adds support for these two elements. However, it outputs other warnings about these elements; see the [corresponding FAQ entry](mkvalidator-WRN201-unknown-element-for-read-profile).
+
+Another possibility of encountering this warning in general is that you're running mkvalidator against a damaged file and that it has found some garbage.
+
+Categories: [mkvalidator](Category-mkvalidator)