I was struggling to get the component registered through html, because you only provided code for building webparts from the codebehind. Funny thing was that there is no intellisense in visual studio but this is working for me.
Is there a description of the properties and tags I can use from within HTML like this:
...
<%
@ Register Tagprefix="radE" Namespace="Telerik.SharePoint" Assembly="RadEditorSharePoint, Version=5.4.0.0, Culture=neutral, PublicKeyToken=1f131a624888eeed" %>
<radE:MOSSRadEditor ID="RuimteBetalendeIntegraties" runat="server" Content='<%#DataBinder.Eval(adapter,"Product.RuimteBetalendeIntegraties")%>' Visible="false" ControlMode="Edit">
</radE:MOSSRadEditor>
<%
--<SharePoint:InputFormTextBox ID="RuimteBetalendeIntegraties" Text='<%#DataBinder.Eval(adapter,"Product.RuimteBetalendeIntegraties")%>'
runat="server" TextMode="MultiLine" Rows='<%#richtTextRows%>' Columns="40" RichText="true"
RichTextMode="FullHtml" AllowHyperlink="true" Visible="false" />
<SharePoint:InputFormTextBox ID="ReRuns" Text='<%#DataBinder.Eval(adapter,"Product.ReRuns")%>'
runat="server" TextMode="MultiLine" Rows='<%#richtTextRows%>' Columns="40" RichText="true"
RichTextMode="FullHtml" AllowHyperlink="true" Visible="false" />--
%>