InDesign INX
From Just Solve the File Format Problem
Adobe InDesign is desktop publishing software. In order to maintain compatibility between versions, InDesign can export into the InDesign Interchange (INX) format.[1][2]
File Information
INX files are in the XML file format. Created for InDesign CS2[3] and replaced in CS4 with IDML.
Specifications
The first line of an INX file is a standard XML declaration that looks like this:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
The next line is an INX-specific processing instruction. It contains information required by InDesign to properly configure the import process. Here is an example:
<?aid style=”33” type="document" DOMVersion="4.0" buildNumber=”225 featureSet="257"?>