| xilinc | Xilize Include |
| xin | OmniMark Include File |
| xje | XJEase Source Code |
| xl | XBLite Source Code |
| xmla | XML for Analysis File |
| xnb | XNA Game Studio Binary Package |
| xob | WeintekHMI EasyBuilder 8000 XOB File |
| xoml | Microsoft Visual Studio Windows Workflow |
| xpb | XPB! Basic Source Code |
| xpk | Xscript Package |
| xpp | X++ Source Code |
| xq | XQuery File |
| xql | XML Query Language |
| xqm | Oxygen XML Editor XQuery Module |
| xquery | XQuery File |
| xqy | XQuery File |
| xrc | wxWidgets XML Based Resource |
| xrd | XRK Data File |
| xrg | Xscript Registry Data |
| xsc | Dataset Designer Internal Data |
| xsc | Xscript Script |
| xss | Dataset Designer Surface Data |
| xst | IBM WebSphere Query Template |
| xsym | CodeWarrior xSYM File |
| xtml | XML4web HTML Document |
| xul | XML User Interface Language File |
| y | Yacc Source |
| yab | Yabasic Source Code |
| yac | Yacc Source |
| yacc | Yacc Source |
| ymx | Yukes 3D Object |
| yobj | Yukes 3D Object |
| ysp | BYOB Sprite |
| yy | GNU Bison Parser |
| zcos | Scilab XML Diagram |
