m-form-error 
Displays a message when the form submission fails. Can only be used inside m-form.
TIP
Template expressions wrapped in double square brackets are supported.
Example 
html
<m-form>
    <m-form-error>[[#error]]incorrect <b>[[title]]</b><br />[[/error]]</m-form-error>
</m-form>html
<m-form>
    <m-form-error></m-form-error>
</m-form>