As far as I see
\lineskip are fixed lengths and don't have any
minus-es, but the distance between lines yet depends on the page. Even after the
\raggedbottom command TeX still could make the interline distance shorter at 100% filled pages and larger at end-of-document or end-of-chapter pages (
\newpage'd or so on). Is there any glue responsible for interline spacing or any command to make it non-expandable and non-compressed ever?
As far as I see
closed as too localized by David Carlisle, Claudio Fiandrino, lockstep, Mensch, Andrew Swann May 21 '13 at 13:06
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there are several factors other than
\lineskip that can affect
the distance between baselines over whole pages.
\parskipis often defined with stretch, so the bottom of a paragraph can be farther from the bottom of the first line of the next paragraph than the nominal
\lineskiplimitcan be applied to add extra space between lines if a line contains a "tall" element, such as a full-size fraction or a matrix.
the baselines of a paragraph aren't "frozen" until the end of a paragraph. however, tex takes an "invisible" paragraph break before display math, and if the type size of the display is changed from the default (usually by making it smaller), the baseline value of the changed size can be applied to the preceding text, (usually) causing the lines in that (partial) paragraph to be closer together than the default baseline value. (many people don't even notice this, but it does cause the overall page to look "funny", and with some experience, one can learn to identify it at a glance.
quotations and footnotes are often set in a size different from that of the main text, with the consequence of different baselines. if it's important that baselines be uniform throughout, special measures must be taken.
in the "ordinary" tex model, display math does not even try to maintain uniform baselines. the tugboat article by kaveh bazergan (mentioned in a comment by Steven Segletes) addresses the matter of how to adhere to a grid that conforms to uniform baselines.
many document classes (at least the ones with which i'm familiar) do not change the page length when a size option (e.g.
[12pt]) is applied to the
\documentclass, so the number of lines placed on the page will not be an exact multiple of
\topskip. in turn, this requires stretch between paragraphs or in display math to achieve
there may be more. if i think of any such conditions, i'll add them to this list.