Last month we started working on a web-based XML editor with just these use cases in mind as part of the ANGLES project, a Digital Humanities Start-Up grant funded by the National Endowment for the Humanities. It is still early days yet but we've made what we feel is a pretty good start. ANGLES extends the ACE editor you mention and connects it, for the moment, to a SAX-style parser to do basic validation. 

The project site for ANGLES is here: and since there's not much there yet, the code is on Github:

As I said, development has just started. We'll be continuing to work on this project through at least Fall 2013 and would love to talk to you (and any other interested parties) about this project.



On Wed, Dec 19, 2012 at 9:31 PM, Brett Zamir <[log in to unmask]> wrote:
On 12/20/2012 6:14 AM, Sebastian Rahtz wrote:
It does seem to me that CodeMirror does not support syntax checking or validation in any way,
have you found some indicator that it can do so? 
The reason I believe CodeMirror can be so blazingly fast with large documents is that it does not reparse the whole document after each change (at least it was this way in version 1). That being said, you can hook up CodeMirror to a well-formedness checker (DOMParser would work fine) or if you have a JavaScript validation library in mind for RelaxNG, etc. to that, and perhaps hook into CodeMirror 3's inline widgets if the checker is line-aware:

it would be just wonderful if you found or made this mythical beast....
Sebastian Rahtz
Director (Research Support) of Academic IT Services 
University of Oxford IT Services
13 Banbury Road, Oxford OX2 6NN. Phone +44 1865 283431