Okay so progress made on getting the validation message in there, although I had to decompile EPiServer.XForms to figure it out.

Added the following:

  <localization fallbackBehavior="Echo, MissingMessage, FallbackCulture" fallbackCulture="en-GB">
    <providers>
      <add virtualPath="~/Resources/LanguageFiles" name="languageFiles" type="EPiServer.Framework.Localization.XmlResources.FileXmlLocalizationProvider, EPiServer.Framework" />
    </providers>
  </localization>

Then dropped in this XML language file in ~/Resources/LanguageFiles/:

<?xml version="1.0" encoding="utf-8" ?>
<languages>
  <language name="English" id="en-GB">
    <xform>
      <datatypes>
        <telephone>
          <inlineerrormessage>
            Not a valid telephone number.
          </inlineerrormessage>
        </telephone>
      </datatypes>
    </xform>
  </language>
</languages>

Onto the next item. :-)

Just for completeness I've udpates the language file based on what I see for other datatypes (using LocalizationService.GetAllStrings("/xform/datatypes");)

<?xml version="1.0" encoding="utf-8" ?>
<languages>
  <language name="English" id="en">
    <xform>
      <datatypes>
        <telephone>
          <caption>Telephone number</caption>
          <inlineerrormessage>
            Not a valid telephone number.
          </inlineerrormessage>
          <summaryerrormessage>
            * is not a valid telephone number.
          </summaryerrormessage>
        </telephone>
      </datatypes>
    </xform>
  </language>
</languages>

Don't know if it is a bug or caching thing but the 'Validate as' field on the form editor doesn't seem to be picking up the caption for my new datatype.

Hi Mark!

I peeked into the code and it seems the UI takes the label from the following path:

/edit/editxform/datatypes/" + typeKey + "/caption"

I have filed the following bug to address this so we use the structure you have used:

Okay, came back to this one today and made more progress with styling. I'm actually replacing the table layout by performing an XSLT transform on the FormDefinition. It doesn't change the mark-up of the fields although I do clear the labels and set my own with handy require field indicator.

I now have:

XFormControl.ControlSetup += XFormControl_ControlSetup;
 
void XFormControl_ControlSetup(object sender, EventArgs e)
{
    var control = (sender as XFormControl);
    control.ClearEventHandlers();
    control.BeforeLoadingForm += control_BeforeLoadingForm;
}
 
void control_BeforeLoadingForm(object sender, LoadFormEventArgs e)
{
    if (!e.EditMode)
    {
        XDocument s = XDocument.Parse(e.FormDefinition);
        XDocument d = new XDocument();
 
        XslCompiledTransform xslt = new XslCompiledTransform(true);
        using (XmlReader xsltReader = XmlReader.Create(GetXsltStream()))
        {
            xslt.Load(xsltReader);
            using (XmlReader reader = s.CreateReader())
            using (XmlWriter writer = d.CreateWriter())
            {
                xslt.Transform(reader, writer);
            }
        }
 
        e.FormDefinition = d.ToString();
    }
}
 
Stream GetXsltStream()
{
    var assembly = Assembly.GetExecutingAssembly();
    var resource = "MyNamespace.XForm.xslt";
 
    return assembly.GetManifestResourceStream(resource);
}

I have this in an initializer but I've just pulled out the relevant parts, you could just as well set it in Global.asax if need.

And my XSLT, although tailored to our solution, looks like:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
    xmlns:xforms="http://www.w3.org/2002/xforms" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <xsl:output method="xml" indent="yes"/>
 
  <xsl:template match="/root">
    <root xmlns:xforms="http://www.w3.org/2002/xforms" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <xsl:copy-of select="./model"/>
      <fieldset id="id_matrix">
        <xsl:apply-templates select=".//td/*" />
      </fieldset>
    </root>
  </xsl:template>
 
  <xsl:template match="td/span">
    <h2>
      <xsl:value-of select="./text()"/>
    </h2>
  </xsl:template>
 
  <xsl:template match="td/xforms:*">
    <div class="form-group">
      <label class="col-md-4 control-label">
        <xsl:attribute name="for">
          <xsl:value-of select="./@ref"/>
        </xsl:attribute>
        <xsl:if test="./@required">
          <em>*</em>
        </xsl:if>
        <xsl:value-of select="./xforms:label/text()"/>
      </label>
      <div class="col-md-8">
        <xsl:apply-templates select="." mode="field" />
      </div>
    </div>
  </xsl:template>
 
  <xsl:template match="td/xforms:submit">
    <xsl:copy>
      <xsl:attribute name="class">btn</xsl:attribute>
      <xsl:apply-templates select="@*|node()" mode="field-copy" />
    </xsl:copy>
  </xsl:template>
 
  <xsl:template match="td/xforms:*" mode="field">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()" mode="field-copy" />
    </xsl:copy>
  </xsl:template>
 
  <xsl:template match="td/xforms:input|td/xforms:select1|td/xforms:textarea" mode="field">
    <xsl:copy>
      <xsl:choose>
        <xsl:when test="./@appearance = 'full'"></xsl:when>
        <xsl:otherwise>
          <xsl:attribute name="class">form-control</xsl:attribute>
        </xsl:otherwise>
      </xsl:choose>
      <xsl:apply-templates select="@*|node()" mode="field-copy" />
    </xsl:copy>
  </xsl:template>
  
  <xsl:template match="@*|node()" mode="field-copy">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()" mode="field-copy" />
    </xsl:copy>
  </xsl:template>
 
  <xsl:template match="td/xforms:*/xforms:label" mode="field-copy" />
 
  <xsl:template match="td/xforms:submit/xforms:label" mode="field-copy">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()" mode="field-copy" />
    </xsl:copy>
  </xsl:template>
 
</xsl:stylesheet>

It's not perfect but it's a lot closer to what we wanted. Hope others find this useful.

Actually one minor tweak to the code:

...
XslCompiledTransform xslt = new XslCompiledTransform(true);
using (Stream stream = GetXsltStream())
using (XmlReader xsltReader = XmlReader.Create(stream))
{
    xslt.Load(xsltReader);
...

Just to make sure we dispose of the stream.