ioccc/markdown.md

IOCCC 29th Markdown Guidelines

Markdown Guidelines Version

These Markdown Guidelines are version 29.0 2025-11-26.

Introduction

The IOCCC makes extensive use of markdown. For example, when submitting to the IOCCC we have people submit remarks about their entry in markdown format. Every winning entry uses a README.md markdown file as the basis for forming the index.html web page for that entry. All HTML 5 generated pages on the Official IOCCC website start with some markdown content. We no longer support older HTML standards and some of our guidelines help integrate winning entries into the website more easily.

See the markdown syntax guide. See also the CommonMark Spec. See the FAQ on "remarks.md submission file".

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.

In the sections below, examples will mark by ❌ for the incorrect method and ✔️ for preferred correct one.

Start remarks.md sections at level 3

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 up to level six:

❌ Reserved in remarks.md only.

# Section Reserved
## Section Reserved

✔ Available every where.

### Section Level 3
#### Section Level 4
##### Section Level 5
###### Section Level 6

Replace <a name="anchor_name"></a> construct.

❌ Incorrect.

<a name="old_way">Section title</a>

✔ Correct.

<div id="new_way"></div>

### Section title

Markdown links instead of <a>...</a>

❌ Incorrect.

This <a href="#link_target>HTML link text</a> works, but we prefer see below...

✔ Correct.

[markdown link text](#link_target)

Replace <strike> or <s>

❌ Incorrect.

<strike>striked through text</strike>
<s>HTML 5 striked through text</s>

✔ Correct.

~~markdown striked through text~~
<del>HTML 5 striked through text</del>

Replace <u>

❌ Incorrect.

<u>old tags</u>

✔ Correct.

<ins>HTML 5 tags</ins>

Replace <tt>

❌ Incorrect.

<tt>obsolete HTML</tt>

✔ Correct.

<span style="font-family: monospace;">monospace font</span>
`markdown style monospace`

Indent code blocks by four spaces, not by TAB.

❌ Incorrect.

echo "This code block is NOT indented"

We request that you indent the code block by multiples of four (4) ASCII SPACES, never TAB (␉):

✔ Correct.

    echo "This code block is indented by multiples 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.

Alternatively its possible to use ``` marks, without the initial four (4) space indentation. This is usually the better method.

✔ Also correct.

```
The same thing applies to any markdown block bracketed by ``` lines.
```

Do not use TAB in markdown files.

Please do NOT indent with ASCII TABs (␉), OR use any ASCII TAB (␉) 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 two (2) or more levels, use multiples of four (4) ASCII SPACES.

❌ Incorrect for markdown files only.

```
␉Please do **NOT**␉use ASCII tabs␉in markdown files.
␉␉Please do **NOT** indent markdown with ASCII tabs.

␉We␉don't␉mind␉tabs␉in␉general,
␉We just ask that you NOT use them in markdown files.
```

✔ Ok for all file types, eg. .c, .h, .mk, .sh, EXCEPT .md markdown files.

␉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.

Use HTML comments for code block language syntax.

We request that fenced markdown code blocks NOT specify a language directly.

❌ Incorrect

```c
    int main(void) {return 0;}
```

Instead, put the language inside an HTML comment, separated from the markdown code block starting fence by a space:

✔ Correct

```<!---c-->
   int main(void) {return 0;}
```

Ensure blank line between code block and text.

❌ Incorrect, missing empty line after closing fence (```).

```
int
main(int foo)
{
   return foo;
}
```
C compilers cannot be given a -Wno-main-arg-errors flag.

✔ Correct, has empty line between closing fence and subsequent text.

```
int
main(int foo)
{
    return foo;
}
```

C compilers cannot be given a -Wno-main-arg-errors flag.

Do not add trailing slash to void HTML tags.

The trailing slash on void HTML elements has no effect and interacts badly with unquoted attribute values; do not use. See also this note on trailing slashes in void-element start tags.

❌ Incorrect

<br/>
<hr/>
<img src="1984-anonymous-tattoo.jpg" alt="image of a tattoo of
the 1984 anonymous C code" width=600 height=401 />

✔ Correct

<br>
<hr>
<img src="1984-anonymous-tattoo.jpg" alt="image of a tattoo of
the 1984 anonymous C code" width=600 height=401>

Do not use a trailing backslash outside of a code block

❌ Incorrect, do not use escaped newlines outside of a code block.

In markdown,\
do NOT use trailing\
backslashes outside of\
a code block

✔ Correct

In markdown,<br>
use trailing<br>
br's outside of<br>
a code block

```
This is OK\
inside a\
markdown code\
block
```

`This is OK\`

Doing it this way will prevent pandoc(1) from generating deprecated HTML elements, such as <br />.

Do not use markdown style images

❌ Incorrect

![alt text](filename.png "Title")

✔ Correct

<img src="filename.png"
alt="describe the filename.png image for someone who cannot view it"
width=PIXEL_WIDTH height=PIXEL_HEIGHT>

Which allows for HTML <img> attributes `alt=`, `width=` and `length=`.

The problem is 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.

Replace 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 <hr />. The <hr /> has no effect in standard HTML 5 and interacts badly with unquoted attribute values.

❌ Incorrect

* * *
- - -
---

✔ Correct

Regular divider...
<hr>

A short divider...
<hr style="width:10%;text-align:left;margin-left:0">

Do not put a literal "(" or ")" in markdown link titles

❌ Incorrect

[some (text)](https://example.com/curds)
[ls(1)](https://example.com/ls-man-page.1)

✔ Correct

[some (text)](https://example.com/curds)
[ls(1)](https://example.com/ls-man-page.1)

Do not end markdown links with "))"

Markdown links that end in "))" complicate parsing and sometimes lead to incorrect URLs or file paths.

❌ Incorrect

[some text](https://example.com/foo_(bar))
This thing, ([some text](some/path)), is NOT ideal.

✔ Correct

[some text](https://example.com/foo_(bar))
This thing, [some text](some/path), is better.

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.

❌ Incorrect

*this text is italic*
***this text is bold italic***

✔ Correct

_this text is italic_
**_this text is bold italic_**
_**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.