This is called outdent (the contrary of indent).
Create a style for these paragraphs. In the
Indent & Spacing tab (
Retraits & espacement in the French locale), set your margins Before/After for the paragraph body, mainly Before, aka. left margin. Give First Line (Première ligne) the negative value of Before. You’re done, no need to tweak tabs.
To use it: style your paragraph with the just created one. Type your “title”, then
Tab which will align you to the paragraph left margin and continue typing as usual.
In case your title is wider than the “margin”, don’t worry. Type
Tab after the “title” (as usual) then
Enter. You’re now on the second line of the same paragraph at left margin.
Tab after the title? This is to cause a “soft” break in text so that justification does not expand spaces in your title up to the right margin. You could, of course, disable this justification in
Compatibility (extend interword spaces on lines with manual newlines) but I find more convenient to keep it enabled so that I control individually which lines are justified and which are not.
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