Tile with a single RichText field in Plone Mosaic with collective.themefragments

fragment.pt

<tal:block define="value nocall:view/data/html|nothing;              
                   output_relative_to nocall:value/@@output_relative_to|nothing"
           condition="output_relative_to"
           content="structure python:output_relative_to(context)" />              

fragment.xml

<?xml version="1.0" encoding="UTF-8"?>
<model xmlns="http://namespaces.plone.org/supermodel/schema"
       xmlns:form="http://namespaces.plone.org/supermodel/form"
       xmlns:marshal="http://namespaces.plone.org/supermodel/marshal"
       xmlns:i18n="http://xml.zope.org/namespaces/i18n"
       i18n:domain="plone">
  <schema>
    <field name="html" type="plone.app.textfield.RichText" marshal:primary="true"
           form:widget="plone.app.z3cform.widget.RichTextFieldWidget">
      <title>Text</title>
    </field>
  </schema>
</model>

versions.cfg

[versions]
plone.tiles = 2.0.0b3
plone.jsonserializer = 0.9.5
plone.app.blocks = 4.1.1
# or newer...