General

You must adhere to the Emacs convention of adding two spaces at the end of every sentence. You should fill your paragraphs to column 70, but under no circumstances should your lines extend past column 79. If your code samples spill over column 79, you should rewrite them.

Tab characters must never appear in the document at all. A REP should include the standard Emacs stanza included by example at the bottom of this REP.

Section Headings

REP headings must begin in column zero and the initial letter of each word must be capitalized as in book titles. Acronyms should be in all capitals. Section titles must be adorned with an underline, a single repeated punctuation character, which begins in column zero and must extend at least as far as the right edge of the title text (4 characters minimum). First-level section titles are underlined with "=" (equals signs), second-level section titles with "-" (hyphens), and third-level section titles with "'" (single quotes or apostrophes). For example:

First-Level Title
=================

Second-Level Title
------------------

Third-Level Title
'''''''''''''''''

If there are more than three levels of sections in your REP, you may insert overline/underline-adorned titles for the first and second levels as follows:

============================
First-Level Title (optional)
============================

-----------------------------
Second-Level Title (optional)
-----------------------------

Third-Level Title
=================

Fourth-Level Title
------------------

Fifth-Level Title
'''''''''''''''''

You shouldn't have more than five levels of sections in your REP. If you do, you should consider rewriting it.

You must use two blank lines between the last line of a section's body and the next section heading. If a subsection heading immediately follows a section heading, a single blank line in-between is sufficient.

The body of each section is not normally indented, although some constructs do use indentation, as described below. Blank lines are used to separate constructs.

Paragraphs

Paragraphs are left-aligned text blocks separated by blank lines. Paragraphs are not indented unless they are part of an indented construct (such as a block quote or a list item).

Inline Markup

Portions of text within paragraphs and other text blocks may be styled. For example:

Text may be marked as *emphasized* (single asterisk markup,
typically shown in italics) or **strongly emphasized** (double
asterisks, typically boldface).  ``Inline literals`` (using double
backquotes) are typically rendered in a monospaced typeface.  No
further markup recognition is done within the double backquotes,
so they're safe for any kind of code snippets.

Block Quotes

Block quotes consist of indented body elements. For example:

This is a paragraph.

    This is a block quote.

    A block quote may contain many paragraphs.

Block quotes are used to quote extended passages from other sources. Block quotes may be nested inside other body elements. Use 4 spaces per indent level.

Literal Blocks

Literal blocks are used for code samples or preformatted ASCII art. To indicate a literal block, preface the indented text block with "::" (two colons). The literal block continues until the end of the indentation. Indent the text block by 4 spaces. For example:

This is a typical paragraph.  A literal block follows.

::

    for a in [5,4,3,2,1]:   # this is program code, shown as-is
        print a
    print "it's..."
    # a literal block continues until the indentation ends

The paragraph containing only "::" will be completely removed from the output; no empty paragraph will remain. "::" is also recognized at the end of any paragraph. If immediately preceded by whitespace, both colons will be removed from the output. When text immediately precedes the "::", one colon will be removed from the output, leaving only one colon visible (i.e., "::" will be replaced by ":"). For example, one colon will remain visible here:

Paragraph::

    Literal block

Lists

Bullet list items begin with one of "-", "*", or "+" (hyphen, asterisk, or plus sign), followed by whitespace and the list item body. List item bodies must be left-aligned and indented relative to the bullet; the text immediately after the bullet determines the indentation. For example:

This paragraph is followed by a list.

* This is the first bullet list item.  The blank line above the
  first list item is required; blank lines between list items
  (such as below this paragraph) are optional.

* This is the first paragraph in the second item in the list.

  This is the second paragraph in the second item in the list.
  The blank line above this paragraph is required.  The left edge
  of this paragraph lines up with the paragraph above, both
  indented relative to the bullet.

  - This is a sublist.  The bullet lines up with the left edge of
    the text blocks above.  A sublist is a new list so requires a
    blank line above and below.

* This is the third item of the main list.

This paragraph is not part of the list.

Enumerated (numbered) list items are similar, but use an enumerator instead of a bullet. Enumerators are numbers (1, 2, 3, ...), letters (A, B, C, ...; uppercase or lowercase), or Roman numerals (i, ii, iii, iv, ...; uppercase or lowercase), formatted with a period suffix ("1.", "2."), parentheses ("(1)", "(2)"), or a right-parenthesis suffix ("1)", "2)"). For example:

1. As with bullet list items, the left edge of paragraphs must
   align.

2. Each list item may contain multiple paragraphs, sublists, etc.

   This is the second paragraph of the second list item.

   a) Enumerated lists may be nested.
   b) Blank lines may be omitted between list items.

Definition lists are written like this:

what
    Definition lists associate a term with a definition.

how
    The term is a one-line phrase, and the definition is one
    or more paragraphs or body elements, indented relative to
    the term.

Tables

Simple tables are easy and compact:

=====  =====  =======
  A      B    A and B
=====  =====  =======
False  False  False
True   False  False
False  True   False
True   True   True
=====  =====  =======

There must be at least two columns in a table (to differentiate from section titles). Column spans use underlines of hyphens ("Inputs" spans the first two columns):

=====  =====  ======
   Inputs     Output
------------  ------
  A      B    A or B
=====  =====  ======
False  False  False
True   False  True
False  True   True
True   True   True
=====  =====  ======

Text in a first-column cell starts a new row. No text in the first column indicates a continuation line; the rest of the cells may consist of multiple lines. For example:

=====  =========================
col 1  col 2
=====  =========================
1      Second column of row 1.
2      Second column of row 2.
       Second line of paragraph.
3      - Second column of row 3.

       - Second item in bullet
         list (row 3, column 2).
=====  =========================

Hyperlinks

When referencing an external web page in the body of a REP, you should include the title of the page in the text, with either an inline hyperlink reference to the URL or a footnote reference (see Footnotes below). Do not include the URL in the body text of the REP.

Hyperlink references use backquotes and a trailing underscore to mark up the reference text; backquotes are optional if the reference text is a single word. For example:

In this paragraph, we refer to the `ROS web site`_.

An explicit target provides the URL. Put targets in a References section at the end of the REP, or immediately after the reference. Hyperlink targets begin with two periods and a space (the "explicit markup start"), followed by a leading underscore, the reference text, a colon, and the URL (absolute or relative):

.. _ROS web site: https://ros.org/

The reference text and the target text must match (although the match is case-insensitive and ignores differences in whitespace). Note that the underscore trails the reference text but precedes the target text. If you think of the underscore as a right-pointing arrow, it points away from the reference and toward the target.

The same mechanism can be used for internal references. Every unique section title implicitly defines an internal hyperlink target. We can make a link to the Abstract section like this:

Here is a hyperlink reference to the `Abstract`_ section.  The
backquotes are optional since the reference text is a single word;
we can also just write: Abstract_.

Footnotes containing the URLs from external targets will be generated automatically at the end of the References section of the REP, along with footnote references linking the reference text to the footnotes.

Text of the form "REP x" or "RFC x" (where "x" is a number) will be linked automatically to the appropriate URLs.

Footnotes

Footnote references consist of a left square bracket, a number, a right square bracket, and a trailing underscore:

This sentence ends with a footnote reference [1]_.

Whitespace must precede the footnote reference. Leave a space between the footnote reference and the preceding word.

When referring to another REP, include the REP number in the body text, such as "REP 1". The title may optionally appear. Add a footnote reference following the title. For example:

Refer to REP 1 [2]_ for more information.

Add a footnote that includes the REP's title and author. It may optionally include the explicit URL on a separate line, but only in the References section. Footnotes begin with ".. " (the explicit markup start), followed by the footnote marker (no underscores), followed by the footnote body. For example:

References
==========

.. [2] REP 1, "REP Purpose and Guidelines", Conley
   (https://ros.org/reps/rep-0001.html)

If you decide to provide an explicit URL for a REP, please use this as the URL template:

https://ros.org/reps/rep-xxxx.html

REP numbers in URLs must be padded with zeros from the left, so as to be exactly 4 characters wide, however REP numbers in the text are never padded.

During the course of developing your REP, you may have to add, remove, and rearrange footnote references, possibly resulting in mismatched references, obsolete footnotes, and confusion. Auto-numbered footnotes allow more freedom. Instead of a number, use a label of the form "#word", where "word" is a mnemonic consisting of alphanumerics plus internal hyphens, underscores, and periods (no whitespace or other characters are allowed). For example:

Refer to REP 1 [#REP-1]_ for more information.

References
==========

.. [#REP-1] REP 1, "REP Purpose and Guidelines", Warsaw, Hylton

   https://ros.org/reps/rep-0001.html

Footnotes and footnote references will be numbered automatically, and the numbers will always match. Once a REP is finalized, auto-numbered labels should be replaced by numbers for simplicity.

Images

If your REP contains a diagram, you may include it in the processed output using the "image" directive:

.. image:: diagram.png

Any browser-friendly graphics format is possible: .png, .jpeg, .gif, .tiff, etc.

Since this image will not be visible to readers of the REP in source text form, you should consider including a description or ASCII art alternative, using a comment (below).

Graphs

ROS REPs support mermaid diagrams [2]

You can create flow charts:

Gantt charts and sequences should also be possible but do not appear to be working.

Comments

A comment block is an indented block of arbitrary text immediately following an explicit markup start: two periods and whitespace. Leave the ".." on a line by itself to ensure that the comment is not misinterpreted as another explicit markup construct. Comments are not visible in the processed document. For the benefit of those reading your REP in source form, please consider including a descriptions of or ASCII art alternatives to any images you include. For example:

.. image:: dataflow.png

..
   Data flows from the input module, through the "black box"
   module, and finally into (and through) the output module.

The Emacs stanza at the bottom of this document is inside a comment.

Escaping Mechanism

reStructuredText uses backslashes ("\") to override the special meaning given to markup characters and get the literal characters themselves. To get a literal backslash, use an escaped backslash ("\\"). There are two contexts in which backslashes have no special meaning: literal blocks and inline literals (see Inline Markup above). In these contexts, no markup recognition is done, and a single backslash represents a literal backslash, without having to double up.

If you find that you need to use a backslash in your text, consider using inline literals or a literal block instead.