make the enum minver greater or equal than the <element> minver

Author: robUx4

specification.markdown

@@ -1161,11 +1161,12 @@ Within an EBML Schema, the XPath of the `@value` attribute is
 `/EBMLSchema/element/restriction/enum/@minver`.
 
 The `minver` (minimum version) attribute stores a nonnegative integer that
-represents the first version of the docType to support the enum value.
+represents the first version of the docType to support the enum value. The value
+**MUST** be greater or equal to the `minver` attribute value of the EBML Element it belongs to.
 
 The `minver` attribute is **OPTIONAL**. If the `minver`
-attribute is not present, then the enum value has a minimum version of
-"1".
+attribute is not present, then the enum value has the same value as the `minver` attribute of the
+EBML Element it belongs to.
 
 ### `<extension>` Element