maybe after that bold and italics but I am not sure really
[X] PNG, including rescale, and the difficult problem of drawing a line without knowing the page width => move that to song rendering?? Or maybe add line length as a parameter in the instrument renderer
[X] CSS for HR
[x] SVG
[x] Do not render gray lines if a line is already user-specified
Support for headings and HR is a minimum
maybe after that bold and italics but I am not sure really