LaTeX
Boxes
Definitions
\makeatletter & \makeatother
\newenvironment & \renewenvironment
Footnotes
Layout
\baselineskip & \baselinestretch
Letters
Line breaking
Math formulas
Dots, horizontal or vertical
Sectioning
\@startsection, typesetting sectional unit headings
\frontmatter, \mainmatter, \backmatter
Spaces
\bigskip & \medskip & \smallskip