The <progress> element indicates the percentage of completion progress of a task.
Possible uses: show uploading progress of a file (non-trivial, but doable) or
showing how far to completion a user is to completing a multi page form.
Attributes include max and value, with progress always being between 0 and 100% complete. The browser calculates the what percentage the value is of the max and adjust the length of the progress bar accordingly.