This needs updating.
Escape sequences (for example "\e[4m" - "underlined", or
"\e[32m" - "set foreground color to green") are translated to
<span> elements with "style" attributes (for example
‘<span style="text-decoration:underline">‘ or ‘<span style="color: green">‘).
After creating such a ‘<span>‘ the current position is moved inside it.
If we’ve previously processed "set foreground color to green", and we see a request for "underlined" it is easy to ceate a nested ‘<span>‘ for the latter. But what if we then see "set foreground color to red"? We don’t want to nest <span style="color: red">‘ inside <span style="color: green">‘ - that could lead to some deep and ugly nesting. Instead, we move the cursor outside bot existing spans, and then create new spans for red and underlined.
The ‘<span>‘ nodes are created lazily just before characters are inserted, by ‘_adjustStyle‘, which compares the current active styles with the desired ones (set by ‘_pushStyle‘).
A possibly better approach would be to match each highlight style into a ‘class‘ attribute (for example ‘green-foreground-style‘ and ‘underlined-style‘). A default stylesheet can map each style class to the correspoding CSS rules. This has the advantage that one could override the highlighting appearance with a custom style sheet.