How tabs are expanded to spaces? I'm confused.

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The spec states that "Tabs in lines are expanded to spaces, with a tab stop of 4 characters". But when I look at the html result. The first tab only got 1 space?

foo→baz→→bim    |  <p>foo baz     bim</p>

[cebe]

The second two tabs also are 5 characters of whitespace.
Looks like it is not to convert each tab into 4 spaces but convert tabs with tab stop of 4 characters.
So the first tab ends after 4 characters, the second ends after 8 and the last after 12 chars.

[appsubscribe]

Thank you @cebe, I got it now :)

[hayd]

The wording in the spec is still confusing (at least to me). Though I get it now, if it helps someone else:

"1\t22\t333\t4444\t5" becomes "1   22  333 4444    5"

It would be great to elaborate this aspect of the spec (not sure if there is a better wording though).