> For the complete documentation index, see [llms.txt](https://overleaf-pro.ayaka.space/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://overleaf-pro.ayaka.space/latex/more-topics/43-table-of-tex-category-codes.md).

# 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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