Wikipedia:Indentation

Good indentation makes prolonged discussions easier to read and understand. It might be helpful to think of discussions as reports with numbered/bulleted sections and subsections where material is not necessarily written in chronological order.

Although this example page about how to indent is an essay, the use of normal indentation is a behavioural guideline that editors are expected to follow. Such guidelines may be enforced by administrative action, especially when other editors have been unable to persuade an individual to abide by them. The guideline should never be used to bite newcomers who don't know how to indent properly, but experienced users are expected to comply with it, to facilitate threaded discussion on talk pages.

This essay only applies to talk pages. Because of differing Cascading Style Sheets between talk pages and other pages, the techniques described in this page are likely to work poorly in other kinds of pages.

Indentation examples
In these examples the boldface line is the most recently added comment.

1. Your reply to a particular comment should be indented beneath that comment. Indents are achieved by typing one or more leading colon   characters at the very left margin, just before the text you add. In the following example, a single colon was typed just before the "Me too" text of the second comment:

2. If you want to reply to a comment, but another editor has already done so, just position your own text beneath that other editor's reply, at the same indentation level:

Note that there is no blank line between comments, and if you reply using multiple paragraphs, use the colons before the blank line between paragraphs (see MOS:LISTGAP for explanation).

3. Your response to a reply should be positioned below that reply, but above any later responses that were made to a different comment. In the following, Alice has done so, using two leading colon characters to indicate that she's responding to the reply made by Bob:

Again, there is no blank line between comments.

4. If you want to introduce a new topic that is still closely related to the one already under discussion, you should add it at the very bottom of the section, below all the previous comments on the original topic, without indenting it at all:

5. When you want to introduce a new topic that isn't closely related to the one already under discussion in a talk-page section, then it's usually best to create an entirely new section or subsection on the talk page for that purpose. You can find out how to do that by reading about "Headings and subheadings" on this page of our concise tutorial for new users. It's also helpful to create new headings and subheadings, as needed, for very long discussion; doing so gives editors the ability to edit only sections of the page, reducing the chance of edit-conflicts that would otherwise occur when two users try to contribute to the same page at the same time.

Outdenting
Sometimes, a long discussion can cause indentation to become too deep, which can make it difficult to read in narrower browser windows. When it does, you should consider outdenting your next comment. When you do that, it's helpful to make clear what you're doing: The templates outdent and outdent2 exist for this purpose. You can use either one, and they can also be employed by their equivalent "shortcut" names of od and od2, respectively.

In the examples below, the user adding the final comment has typed the characters of the template, including its "braces", at the left margin, below the preceding comment, and just ahead of the text they entered for their own comment:

Example of outdent

Example of outdent2

What kind of markup is this, anyway?
This is wikitext. Wikipedia has never had a set of markup specifically designed for use in talk pages. Editors appropriated markup that was intended for other purposes for use in talk pages. There was a project, Flow, intended to view and contribute to talk pages, but this project was uninstalled from English Wikipedia in November 2016, by request of the community.

The appropriated markup is intended for lists. Perhaps the most common departure from proper list markup is the use of. In definition lists, a  at the beginning of the line indicates a term which is to be defined, and   at the beginning of the next line indicates the definition of the term. But in talk pages  is seldom used.