Table of TeX category codes

Category code	Description	Standard LATEX/TEX
0	Escape character—tells TEX to start looking for a command	`\`
1	Start a group	{
2	End a group	}
3	Math shift—switch in/out of math mode	$
4	Alignment tab	&
5	End of line	ASCII code 13 (`\r`)
6	Macro parameter	#
7	Superscript—for typesetting math: $y=x^2$ $y=x^2$	ˆ
8	Subscript—for typesetting math: $y=x_2$ $y=x_2$	_
9	Ignored character	ASCII 0 `<null>`
10	Spacer	ASCII codes 32 (space) and 9 (tab character)
11	Letter	A...Z, a...z, (and thousands of Unicode characters)
12	Other	0...9 plus ,.;?" and many others
13	Active character	Special category code for creating single-character macros such as ˜
14	Comment character—ignore everything that follows until the end of the line	%
15	Invalid character, not allowed to appear in the .tex input file	ASCII code 127 (`DEL`)

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