Additive animation of text x and y with tspan
Four values animations are added with additive sum for
x and y of text ('abcd') and tspan inside ('bc', without explicitly
set x and y). The absolute initial position of each glyph is
therefore defined by the x/y lists of the text element.
The visible result
is that the blue 'abcd' covers exactly the red 'abcd' without
any visible animation effect.
If something red gets visible, this indicates an error.
a
b
c
d
abcd