code: private XML checksAttributesExistence(Class<?> aClass,String[] attributes){
  		if(!classExists(aClass)) Error.xmlClassInexistent(this.xmlPath,aClass);
  		for (String attributeName : attributes) 
  			try{ 				 aClass.getDeclaredField(attributeName);		  }
  			catch (Exception e){ Error.attributeInexistent(attributeName, aClass);}
  		return this;
  	}
docs: Verifies that the attributes exist in aClass.
  @param aClass Class to check
  @param attributes list of the names attributes to check.
  @return this instance of XML