XPontus

XPontus is an open source XML editor. It may be possible to adapt XPontus code to provide validation capabilities.

XPontus does XML well-formness validation as well as schema based validation.

<disposition_code>60</disposition_code
</line_item>

Error at line:109,column:5
The end-tag for element type "disposition_code" must end with a '>' delimiter.

<disposition_code>60
</line_item>

Error at line:109,column:7
The element type "disposition_code" must be terminated by the matching end-tag "</disposition_code>".

<disposition_code></disposition_code>

The document is invalid!
Error around line : 108,column:46
Content of element "disposition_code" is incomplete

XPontus also has a pretty print function that indents and inserts newlines.