Is symbolic icons ever standard?

[Nikita Zlobin]

I got first try with symbolic svg icons when used zenity to create
handcrafted internet connection tracker, employing information/error
dialogs of different color schemas (green and red), with icon to be
colored respectively.

Now I search for exact info about how such icons are created, in order
to know, what code must do in order to handle them correctly. First
time I visited some page, telling about special color values in svg
code, which are to be replaced to actual foreground, background or
other colors, according to style.

Now - all I could find is this page:
https://wiki.gnome.org/Design/OS/SymbolicIcons

It has links to other pages named "SymbolicIcons", but both are removed
(one from freedesktop, second from gnome whiteboard). Only link to two
librsvg bugs hinted me, that it is done by using special color values,
e.g. black for background (I thought it must be some variable names).

Is it ever approved standard or it's now treated same way as gtk
csd/headerbar?

Could it be that gnome decided to receive it for gnome specific, given
that nothing similar can be found in qt or other apps, prefering cairo
over raw x11 or wayland without even gdk (such as rofi, dunst, i3wm)?