validating xml

[jbv]

Hello list

I have a script server-side that sends xml data to a web page.
The xml content is enriched text (featuring several html tags) made by
other users and stored in a DB.
When enriching text with a js library, it often happens that something
goes wrong with tags... So my question : is there a way (function, LC or
PHP library, whatever) to check if the xml is well-formed (all tags
closed, etc), and possibly fix it, before sending it to the client browser
or app ?

Thanks in advance
jbv