Comments regarding 7.1.4 Captions characteristics
A comma sign (",") seems to be missing in the following sentence (NOTE 1) of EN301549 clause 7.1.4, right after the word "size":
"Defining the background and foreground colour of subtitles, font type, size opacity of the background box of subtitles, and the contour or border of the fonts can contribute to meeting this requirement."
(Otherwise: What is "size opacity"?)