Hi 
Is this possible in Libre Writer? How?
It would be great to be able to have sub TOCs in a bigger document.
Greetings,
Klaus
That depends on your document structure. Writer uses “levels” to classify the content of your document. Those levels are associated with paragraph styles and you can see them in Tools → Chapter numbering. By default, you have each level associated to a heading style (Level 1 → Heading 1, etc.). You can create sub-TOCs that collect all sub-levels bellow each Level 1: when inserting the TOC, just select “per chapter” under the “Type” tab.