An RML file is an annotation file created and used by Volo View application by Autodesk. It contains annotation information and text marks to be overlaid on the drawing for taking notes. These annotations are displayed in red text over the drawing and that is why the name Redline Markup Language file. Volo View has been discontinued and is no more supported by Autodesk. RML files contents are embedded in CAD drawings as notes.
RML File Format
RML files are created and saved to disc in XML file format which is a universal file format for exchange of data. It is in human readable format and can be opened with any text editor such as Microsoft Notepad, Notepad++, and Apple TextEdit.