New posts in Optional Arguments

Xparse's new e-type argument (replacement for k-type argument)

Newcommand with different definitions depending on the value of one argument

How to write macro with variable amount of text variables

How do I nest a command with an optional argument?

newcommand with comma separated argument, and optional arguments

number of arguments that is a multiple of a number in a macro for curves with continuously varying thickness

How is beamer's {frame} title optional, yet in braces (not brackets)?

Special behavior if optional argument is not passed

How to define a new command based on \section with its optional argument?

Cannot use ampersand as argument in user defined command with optional arguments