| \documentclass{article} | |
| \newcommand{\foo}{} | |
| \renewcommand*{\foo}[1]{#10} | |
| \providecommand{\foo}[1][default]{#11} | |
| \newenvironment*{baz}{START}{STOP} | |
| \renewenvironment{baz}[1]{HEAD of #12:}{TAIL} | |
| \renewenvironment*{baz}[1][default]{BEGINNING of #12:}{END} | |
| \begin{document} | |
| \foo{TeX} % -> TeX0 | |
| \begin{baz} tex \end{baz} % -> BEGINNING of default2:tex END | |
| \end{document} |