12.1.1 Control sequence, control word and control symbol

When reading input TeX converts the stream of read characters into a sequence of tokens. When TeX sees a backslash \, it will handle the following characters in a special way in order to make a control sequence token.

The control sequences fall into two categories:

The sequence of characters so found after the \ is also called the control sequence name.

Blanks after a control word are ignored and do not produce any whitespace in the output (see \newcommand & \renewcommand and Backslash-space, \ ).

Just as the \relax command does nothing, the following input will simply print ‘Hello!’ :


This is because blanks after \relax, including the newline, are ignored, and blanks at the beginning of a line are also ignored (see Leading blanks).

Unofficial LaTeX2e reference manual