# IOCCC 28th Markdown Guidelines
## IOCCC Markdown guidelines version

These [IOCCC markdown guidelines](markdown.html) are version **28.4 2025-04-28**.

**IMPORTANT**: Be sure to read the [IOCCC rules](next/rules.html) and [IOCCC guidelines](next/guidelines.html). Jump to: [top](#)
## IOCCC Markdown Guidelines Introduction
The IOCCC makes extensive use of [markdown](https://daringfireball.net/projects/markdown/). For example, when submitting to the IOCCC we have people submit remarks about their entry in markdown format. Every [winning IOCCC entry](years.html) uses a `README.md` markdown file as the basis for forming the `index.html` web page for that entry. All generated HTML pages on the [Official IOCCC website](https://www.ioccc.org/index.html) start with some markdown content. See the [markdown syntax](https://www.markdownguide.org/basic-syntax) guide. See also the [CommonMark Spec](https://spec.commonmark.org/current/). See the FAQ on "[remarks.md submission file](faq.html#remarks_md)". Nevertheless, the IOCCC does have certain practices that we ask authors to follow. Some of these relate to use of markdown directly and others relate to injecting HTML into the markdown file. Jump to: [top](#)
## Please DO start `remarks.md` sections at level 3 (`###`), increasing for subsections up to 6 (`######`)
IF (it is not required) you do use sections in your `remarks.md` file (this does not apply to other markdown files), **PLEASE** start at level three: ``` # Foo <=== no thank you ## Foo <=== no thank you ``` Instead, start sections with 3 `#`s: ``` ### Section 0 ``` For each subsection of the current section, add another `#`, up to 6, going back to 3 for new sections. For instance: ``` ### Section 0 ... #### 1st subsection of section 0 ... ##### 1st sub-subsection of the 1st subsection of section 0 ... #### 2nd subsection of section 0 ... ##### 1st sub-subsection of the 2nd subsection of section 0 ... ##### 2nd sub-subsection of the 2nd subsection of section 0 ... ###### 1st sub-sub-subsection of the 2nd sub-subsection of the 2nd subsection of section 0 ... ### Section 1 ... ### Section 2 ... Etc. ```
## Please do NOT use the `name` attributes in HTML `...` hyperlink elements
Please do **NOT** use the HTML construct: ``` ... <=== no thank you ``` as those are **NOT** part of the HTML 5 standard. Instead use: ```
...
``` where the `...` is the HTML you want to "name". The `
` encapsulates the HTML you want to name: i.e., the target of some `` or some other `` for the given page URL. ### IMPORTANT POINT: There are certain markdown constructs that **CANNOT** have an **internal** `
...
` element. An example is headings (lines that start with a `#`). For example: ``` #
THIS WILL NOT WORK!
<=== this will not work ``` For things like headings, you have to surround them with the `
...
` element, as in: ```
# This will work
``` While some browsers will still recognize the HTML construct `...`, it is possible **they MIGHT NOT** in the future. Jump to: [top](#) It is easier and preferred to use markdown links rather than HTML `..` anchors. Instead of: ``` Use of
## Please do NOT use the `` or the `` HTML element
Please do **NOT** use the obsolete `` or the obsolete `` (**strikeout**) HTML elements: ``` ... <=== no thank you ... <=== no thank you ``` Use instead: ``` ... ``` Jump to: [top](#)
## Please do NOT use the `` HTML element
Please do **NOT** use the obsolete `` (_underline_) HTML element: ``` ... <=== no thank you ``` Use instead: ``` ... ``` Jump to: [top](#)
## Please do NOT use the `` HTML element
Please do **NOT** use the obsolete `` (**teletype**) HTML element: ``` The tt element is obsolete <=== no thank you ``` Instead use either a monospaced `` or an inline markdown code block: ``` Use of a monospaced font is one option, however ... ``` We recommend using the inline markdown code block method instead: ``` Using the `inline markdown code block` is easier and is **preferred**. ``` Jump to: [top](#)
## Please do NOT use unindented code blocks
Please do **NOT** start code blocks at the first column. For example: ```` ``` <%%NO_COMMENT%%!---sh--> echo "This code block is NOT indented" <=== no thank you ``` ```` We request that you indent the code block by multiples of 4 ASCII **SPACES**: ```` ``` <%%NO_COMMENT%%!---sh--> echo "This code block is indented by mutiples of 4 spaces" # The top level starts with a 4 ASCII space indent. # # Only indent with multiples of 4 ASCII spaces. # 2nd level indent needs 8 ASCII spaces (no tabs). # 3rd level indent needs 12 ASCII spaces (no tabs). # etc. ``` ```` Moreover: ```` ``` The same thing applies to any markdown block surrounded by ``` lines. ``` ```` Please do **NOT** indent using ASCII tab characters in markdown files. Jump to: [top](#)
## Please do NOT use ASCII tabs in markdown files
Please do **NOT** indent with ASCII tabs, **OR** use any ASCII tab characters anywhere inside a markdown file. While we have nothing against the ASCII tab character in general, we have discovered that ASCII tab characters create problems when used as part of the leading whitespace within a markdown file. If you need to indent 2 or more levels, use multiples of 4 ASCII **SPACES**. For example: ```` ``` Please do **NOT** use ASCII tabs in markdown files. <=== no thank you Please do **NOT** indent markdown with ASCII tabs. <=== no thank you We don't mind tabs in general, <=== no thank you We just ask that you NOT use them in markdown files. ``` ```` And to clarify, we are only talking about markdown files, not C code or any other non-markdown content: ```` printf("It is fine to use tabs in Obfuscated C code.\n"); /* if you wish */ // We ask that you to NOT use ASCII tab characters in your remarks.md writeup, // or in any other markdown files within your entry, please. ```` **NOTE**: Again, you are **perfectly welcome** to use ASCII tab characters in your C code and other non-markdown files. We simply ask that you do **NOT** use any ASCII tab characters in markdown files. Jump to: [top](#)
### Tip for `vim` users
If you use `vim` you can put in your `.vimrc` file (usually `~/.vimrc`) the following settings to make sure the tabs are not put in without you noticing: ``` set tabstop=8 " a tab is 8 spaces (or whatever you wish it to be set to) set softtabstop=4 " ...but when inserting/backspacing use 4 spaces set shiftwidth=4 " ...and auto-indent 4 spaces (when autoindent is set) set expandtab " ...expand tab into spaces ``` If you have file type detection enabled you can, if you prefer, have these settings set just for markdown files: ``` autocmd! Filetype markdown setlocal set tabstop=8 softtabstop=4 shiftwidth=4 expandtab ``` or so. This will prevent the tab key from inserting tabs; rather it will insert 4 spaces. To **VERIFY** that there are no tabs in a file you may do, in command mode: ``` /\t ``` If you're in insert mode hit `ESC` first. Jump to: [top](#)
## Please use HTML comments to specify a language for a code block
We request that [fenced markdown code blocks](https://www.markdownguide.org/extended-syntax/#fenced-code-blocks) **NOT** specify a language directly. For example: ```` ```c <=== no thank you int main(void) {return 0;} ``` ```` Instead, put the language inside an HTML comment, separated from the markdown code block starting fence by a space: ```` ``` <%%NO_COMMENT%%!---c--> int main(void) {return 0;} ``` ```` **IMPORTANT**: The **initial**   **\` \` \`**   must be followed by an **ASCII SPACE**, and **THEN** an **opening** **``" (two "`-`"s followed by a "`>`"). Jump to: [top](#)
## Please do NOT add trailing slash to void HTML elements
Please do **NOT** use a trailing slash on [void HTML elements](https://github.com/validator/validator/wiki/Markup-»-Void-elements). See also this note on [trailing slashes in void-element start tags](https://github.com/validator/validator/wiki/Markup-»-Void-elements#trailing-slashes-in-void-element-start-tags-do-NOT-mark-the-start-tags-as-self-closing). The trailing slash on void HTML elements has no effect and interacts badly with unquoted attribute values. For example, please do **NOT** use markdown like these: ```
<=== no thank you
<=== no thank you image of a tattoo of the 1984 anonymous C code <=== no thank you ``` Instead use, respectively: ```
image of a tattoo of the 1984 anonymous C code ``` Jump to: [top](#)
## Please do NOT use a TRAILING backslash (`\`) outside of a code block
Unless the line is inside a markdown code block, please do **NOT** end a markdown line with a trailing backslash (`\`). Instead use a trailing `
`. Instead of: ``` In markdown,\ <=== no thank you do NOT use trailing\ backslashes outside of\ a code block ``` use: ``` In markdown,
use trailing
br's outside of
a code block ``` Again, use of a trailing backslash (`\`) inside a markdown code block is fine: ```` ``` This is OK\ inside a\ markdown code\ block ``` ```` as is: ``` `This is OK\` ``` Doing it this way will prevent `pandoc(1)` from generating deprecated HTML elements such as `
`. Jump to: [top](#)
## Please do NOT use markdown style images
Please do **NOT** use the markdown embedded image element. Instead of using this markdown element to embed an image: ``` ![alt text](filename.png "Title") <=== no thank you ``` Use an `` HTML element with `alt=`, `width=` and `length=` attributes: ``` describe the filename.png image for someone who cannot view it ``` For example, instead of: ``` ![1984-anonymous-tattoo.jpg](1984-anonymous-tattoo.jpg) <=== no thank you ``` use this HTML: ``` image of a tattoo of the 1984 anonymous C code ``` The problem goes beyond the fact that `pandoc(1)` generates problematic HTML from the markdown image construct, the resulting HTML does **NOT** have `width` and `height` information so browsers have to slow down on rendering text around the image until it can internally determine the image size. Jump to: [top](#)
## Please do NOT use markdown style horizontal lines
Please do **NOT** use `---` style lines in markdown to create horizontal lines or to separate sections. Unless something is inside a markdown **code block**, do **NOT** start a line with 3 or more dashes ("`-`"s). Such markdown causes `pandoc(1)` to generate `
`. The `
` has no effect in standard HTML 5 and interacts badly with unquoted attribute values. If a horizontal line is really needed, use: ```
``` If a short line is needed, use: ```
``` Jump to: [top](#)
## Please do NOT put a LITERAL "`(`" or "`)`" in markdown link titles
Please do **NOT** use literal parentheses inside markdown link titles. Instead of: ``` [some (text)](https://example.com/curds) <=== no thank you ``` use: ``` [some (text)](https://example.com/curds) ``` Instead of: ``` [ls(1)](https://example.com/ls-man-page.1) <=== no thank you ``` use: ``` [ls(1)](https://example.com/ls-man-page.1) ``` Jump to: [top](#)
## Please do NOT end markdown links with "`))`"
Please do **NOT** end a markdown link with a double closed parenthesis "`))`". Markdown links that end in "`))`" complicate parsing and sometimes lead to incorrect URLs or file paths. Instead of: ``` [some text](https://example.com/foo_(bar)) <=== no thank you ``` use: ``` [some text](https://example.com/foo_(bar)) ``` As another example, instead of: ``` This thing, ([some text](some/path)), is NOT ideal. <=== no thank you ``` use: ``` This thing, [some text](some/path), is better. ``` Jump to: [top](#)
## Please do NOT place text on the IMMEDIATE (very next) line after a markdown code block
Please do **NOT** place text on the next line after a markdown code block. Instead, place a blank line after the end of a markdown code block as this makes it easier to detect when markdown code blocks are **NOT** properly indented. Instead of: ```` ``` int main(int foo) { return foo; } ``` C compilers cannot be given a -Wno-main-arg-errors flag. <=== no thank you ```` use: ```` ``` int main(int foo) { return foo; } ``` C compilers cannot be given a -Wno-main-arg-errors flag. ```` **BTW**: Please note the blank line after the code block. Jump to: [top](#)
## Please use `_` for italics in markdown
Please do **NOT** use `*` (single asterisk) for italics in markdown. Instead use an underscore (`_`). Using an asterisk can complicate parsing and sometimes lead to incorrect results. This can especially go for when it is **_bold and italic_**. For example, instead of: ``` *this text is italic* <=== no thank you ``` use: ``` _this text is italic_ ``` Another example, for **_bold italic_**: Do **NOT** use: ``` ***this text is bold italic*** <=== no thank you ``` Instead use: ``` **_this text is bold italic_** ``` or: ``` _**this text is bold italic**_ ``` **BTW**: the astute reader might notice that some cases of `*` for italic might have slipped through. We do ask you, however, to please observe this rule, as best you can.