Sizing by attribute should be optional.

[lastobelus]

Sizing by width / height makes styling by css difficult; also icons don't scale with user style sheets.

width/height bindings should be optional, and the base style be something like:

.ion__svg {
    overflow: visible;
    display: inline-block;
    height: 1em; /* possibly tweaked so icons match typical font x-heights; I use 1.1em along with margin-top: .05em */
    font-size: inherit;
}