code: private XML checksGlobalExistence(Class<?> aClass){
  		if(!classExists(aClass)) Error.xmlClassInexistent(this.xmlPath,aClass);
  		if(findXmlClass(aClass).global==null)
  			Error.xmlGlobalInexistent(aClass);
  		return this;
  	}
docs: Verifies that the global mapping exist in aClass.
  @param aClass class to check
  @return this intance of XML