Strange rendering behavior with CSS property "content"

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Highlighted
Occasional Visitor

I found the problems when using MathJax, original issue: https://github.com/mathjax/MathJax/issues/2440

At first, I think it's the problem of MathJax, but after some tests, it turned out to be some bugs (features???) in Edge. It seems to have something to do with the CSS property "content":

Here are two tests.

<!doctype html>
<html>
    <head>
        <style>
            .a::before { content: "a"; } .b::before { content: "b"; } .c::before { content: "c"; } .d::before { content: "d"; } .e::before { content: "e"; } .f::before { content: "f"; } .g::before { content: "g"; } .h::before { content: "h"; } .i::before { content: "i"; } .j::before { content: "j"; } .k::before { content: "k"; } .l::before { content: "l"; } .m::before { content: "m"; } .n::before { content: "n"; } .o::before { content: "o"; } .p::before { content: "p"; } .q::before { content: "q"; } .r::before { content: "r"; } .s::before { content: "s"; } .t::before { content: "t"; } .u::before { content: "u"; } .v::before { content: "v"; } .w::before { content: "w"; } .x::before { content: "x"; } .y::before { content: "y"; } .z::before { content: "z"; } .A::before { content: "A"; } .B::before { content: "B"; } .C::before { content: "C"; } .D::before { content: "D"; } .E::before { content: "E"; } .F::before { content: "F"; } .G::before { content: "G"; } .H::before { content: "H"; } .I::before { content: "I"; } .J::before { content: "J"; } .K::before { content: "K"; } .L::before { content: "L"; } .M::before { content: "M"; } .N::before { content: "N"; } .O::before { content: "O"; } .P::before { content: "P"; } .Q::before { content: "Q"; } .R::before { content: "R"; } .S::before { content: "S"; } .T::before { content: "T"; } .U::before { content: "U"; } .V::before { content: "V"; } .W::before { content: "W"; } .X::before { content: "X"; } .Y::before { content: "Y"; } .Z::before { content: "Z"; }
        </style>
    </head>
    <body>
        <span class="A"></span><span class="B"></span><span class="C"></span><span class="D"></span><span class="E"></span><span class="F"></span><span class="G"></span><span class="H"></span><span class="I"></span><span class="J"></span><span class="K"></span><span class="L"></span><span class="M"></span><span class="a"></span><span class="b"></span><span class="c"></span><span class="d"></span><span class="e"></span><span class="f"></span><span class="g"></span><span class="h"></span><span class="i"></span><span class="j"></span><span class="k"></span><span class="l"></span><span class="m"></span><span class="n"></span><span class="o"></span><span class="p"></span><span class="q"></span><span class="r"></span><span class="s"></span><span class="t"></span><span class="u"></span><span class="v"></span><span class="w"></span><span class="x"></span><span class="y"></span><span class="z"></span><span class="N"></span><span class="O"></span><span class="P"></span><span class="Q"></span><span class="R"></span><span class="S"></span><span class="T"></span><span class="U"></span><span class="V"></span><span class="W"></span><span class="X"></span><span class="Y"></span><span class="Z"></span>
    </body>
</html>

Firefox:

f-e1.png

 Edge:

e-e1.png

 

<!doctype html>
<html>
    <head>
        <style>
            .a::before { content: "a"; } .b::before { content: "b"; } .c::before { content: "c"; } .d::before { content: "d"; } .e::before { content: "e"; } .f::before { content: "f"; } .g::before { content: "g"; } .h::before { content: "h"; } .i::before { content: "i"; } .j::before { content: "j"; } .k::before { content: "k"; } .l::before { content: "l"; } .m::before { content: "m"; } .n::before { content: "n"; } .o::before { content: "o"; } .p::before { content: "p"; } .q::before { content: "q"; } .r::before { content: "r"; } .s::before { content: "s"; } .t::before { content: "t"; } .u::before { content: "u"; } .v::before { content: "v"; } .w::before { content: "w"; } .x::before { content: "x"; } .y::before { content: "y"; } .z::before { content: "z"; } .A::before { content: "A"; } .B::before { content: "B"; } .C::before { content: "C"; } .D::before { content: "D"; } .E::before { content: "E"; } .F::before { content: "F"; } .G::before { content: "G"; } .H::before { content: "H"; } .I::before { content: "I"; } .J::before { content: "J"; } .K::before { content: "K"; } .L::before { content: "L"; } .M::before { content: "M"; } .N::before { content: "N"; } .O::before { content: "O"; } .P::before { content: "P"; } .Q::before { content: "Q"; } .R::before { content: "R"; } .S::before { content: "S"; } .T::before { content: "T"; } .U::before { content: "U"; } .V::before { content: "V"; } .W::before { content: "W"; } .X::before { content: "X"; } .Y::before { content: "Y"; } .Z::before { content: "Z"; }
        </style>
    </head>
    <body>
        <span class="a"></span><span class="b"></span><span class="c"></span><span class="d"></span><span class="e"></span><span class="f"></span><span class="g"></span><span class="h"></span><span class="i"></span><span class="j"></span><span class="k"></span><span class="l"></span><span class="m"></span><span class="n"></span><span class="o"></span><span class="p"></span><span class="q"></span><span class="r"></span><span class="s"></span><span class="t"></span><span class="u"></span><span class="v"></span><span class="w"></span><span class="x"></span><span class="y"></span><span class="z"></span><span class="A"></span><span class="B"></span><span class="C"></span><span class="D"></span><span class="E"></span><span class="F"></span><span class="G"></span><span class="H"></span><span class="I"></span><span class="J"></span><span class="K"></span><span class="L"></span><span class="M"></span><span class="N"></span><span class="O"></span><span class="P"></span><span class="Q"></span><span class="R"></span><span class="S"></span><span class="T"></span><span class="U"></span><span class="V"></span><span class="W"></span><span class="X"></span><span class="Y"></span><span class="Z"></span>
    </body>
</html>

Firefox:

f-e2.png

Edge:

e-e2.png