Since version 1.1.0, generated html for ttml span contains one <span> per character.

For what I understand, textCombine style should be used only in the context of a vertical writing mode.
But it seems that we always go into this part of the code whether we are writing horizontally or not

See ttml file example provided
sub_eng_short.xml.zip

For example
TTML code
<span style="s1">eng : 00:00:00.000</span>

Generated html code
<span style="margin: 0px; color: rgb(255, 255, 0); direction: ltr; font-family: sans-serif; font-size: 46px; font-style: normal; font-weight: normal; text-decoration: none; text-combine-upright: none; unicode-bidi: normal; visibility: visible; white-space: nowrap;"><span>e</span><span>n</span><span>g</span><span> </span><span>:</span><span> </span><span>0</span><span>0</span><span>:</span><span>0</span><span>0</span><span>:</span><span>0</span><span>1</span><span>.</span><span>0</span><span>0</span><span>0</span></span>