Display one or more error messages associated with this field, using {@link #msgTarget} to determine how to
display the messages and applying {@link #invalidCls} to the field's UI element.

**Note**: this method does not cause the Field's {@link #validate} or {@link #isValid} methods to return `false`
if the value does _pass_ validation. So simply marking a Field as invalid will not prevent submission of forms
submitted with the {@link Ext.form.action.Submit#clientValidation} option set.

@param {String/String[]} errors The validation message(s) to display.
function(errors) {
        // Save the message and fire the 'invalid' event
        var me = this,
            oldMsg = me.getActiveError(),
            active;
            
        me.setActiveErrors(Ext.Array.from(errors));
        active = me.getActiveError();
        if (oldMsg !== active) {
            me.setError(active);
        }
    }