Invalid ID attribute value

[RazrFalcon]

By the XML/HTML/SVG spec the id attribute

must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

But in the src/gtk/assets.svg filter id's are set to 1 and 2 which is incorrect and may cause rendering errors. Also, rect's with 16x16, 21x21, etc.

There are a lot more warnings that you can check via https://validator.w3.org/.

[nana-4]

Now I've fixed it (except for Inkscape-specific error/warning which even pure Inkscape SVG has).

Thanks for pointing it out!