What should I enter in the 'document comments' field when uploading a document? 

You should enter a meaningful description of the file you are uploading, for example: 'Front elevation part 1'. 

You may also find it useful for consistency to make the document comment match the filename. 

For detailed guidance on supporting documents, read our application guidance¹ for help submitting online using Planning Portal Wales.

1. https://www.planningportal.co.uk/wales/services-and-information/help/making-a-planning-application-in-wales/attach-supporting-files