Edit online

DITA_OT_DIR refers to the default directory that is specified for your DITA Open Toolkit distribution in the Options > Preferences > DITA preferences page.

For example, if you are using DITA OT 3.3.1 that comes bundled with Oxygen XML Editor, the default directory is: [OXYGEN_INSTALL_DIR]/frameworks/dita/DITA-OT3.x. You can also specify a custom directory.