Looking through the questions we have so far, I'm noticing the different ebook formats being written in multiple different ways.

In some cases, I'm seeing them written as file extensions such as .epub, while other forms are epub, ePub, and EPUB. Similarly for Mobi (.mobi, mobi, Mobi, MOBI) and PDF (.pdf, pdf, PDF).

I'm wondering if one of the things we should consider establishing is a convention for how these are written. Do we use the file extension form, an all lowercase form, an all uppercase form, or some other proper form of the name?

It's a little jarring seeing these few formats written multiple different ways, and I think establishing and holding to a convention could make reading questions and answers that much easier.

  • I certainly think the dot is important. My personal preference is for all caps. Jan 7, 2014 at 7:51
  • actually from the point of view of a search engine, all forms are equivalent.
    – mau Mod
    Jan 7, 2014 at 10:18
  • 1
    @mau - true, but being a site related to publishing, style matters even more :)
    – DVK
    Jan 7, 2014 at 16:13
  • 1
    How would we police this - we would end up doing many small edits
    – mmmmmm
    Jan 12, 2014 at 19:33

4 Answers 4


I personally find when people decide to edit my posts to change what I typed to some arbitrary standard that does not add to the post or the readability of the post, I get very annoyed. These seem to be edits for the sake of editing and should be avoided.

To this point I have seen no arguement for standardizing this other than conformity. There is little chance of misunderstanding MOBI vs .MOBI vs .mobi and thus the standard adds no real value. Things like this can turn off new users that we are trying to attract to the site.

So in short My Vote is NO we should not have a convention.


As I have just seen the changes to this revision and they are not consistent with my experience on SO and other SE sites (of course they don't have to be).

I would like to propose to restrict the preformatted text to actual file names, file name parts, or file content, and particularly not apply them to acronyms:

  • diary.epub is an example of an .epub file.
  • Its CSS stylesheet starts with:

    @namespace h "http://www.w3.org/1999/xhtml";
    .blockquote {
        display: block;
        margin-bottom: 0.1em;
        margin-left: 1.5em;
        margin-right: 1.5em;
        margin-top: 0.8em
  • CSS, EPUB are acronyms and are not blockquoted (i.e. don't use EPUB)

  • I would roll that revision back, and probably to the first revision. The trouble is that both edits are too minor so revering is not good, and as one is by a moderator I would like to know @EdCottrell s reason and where dow this edit match the discussion in meta
    – mmmmmm
    Mar 8, 2014 at 19:55

I would propose:

  • Use blockquote formatting. It's a good convention for filenames often used on SO

  • Use dots. They unambiguously indicate that it's an extention/type (especially when the same word can be referring to a company such as Mobi).

  • use lower case because most ebooks have lower case extension (I don't have proof, just my personal observation. if you really care, it'd make an interesting question for the main site).


  • .mobi
  • .pdf
  • Don't use code formatting or block quote for individual words it makes text harder to read.
    – mmmmmm
    Jan 8, 2014 at 14:47
  • I also prefer lowercase, highlighted and dotted filenames
    – Sekhemty
    Jan 8, 2014 at 17:58
  • 1
    Code formatting has a semantic implication: screen readers will likely attempt to "spell out" the extension, which they likely would not do otherwise. Jan 8, 2014 at 21:53
  • What would you use for Kindle format files?
    – mmmmmm
    Jan 12, 2014 at 19:32
  • Also highlighting single words makes things less readable
    – mmmmmm
    Jan 12, 2014 at 19:34
  • @Mark - I'm not too familiar with Kindle but I thought they have their own format (azw3?)
    – DVK
    Jan 12, 2014 at 19:34
  • @Mark - you made the "harder to read" comment twice :) - but it would be nice to offer evidence in the form of studies or a caveat that it's your own personal opinion.
    – DVK
    Jan 12, 2014 at 19:35
  • @DVK that is one version of it - and using the logic in this question we would use .azw3 rather than Kindle format - which is more usable to those reading
    – mmmmmm
    Jan 12, 2014 at 19:35
  • @Mark - depends on context. If we are discussing files in that format, then the extension form. If generic Kindle books, then "Kindle ebooks" seems more appropriate.
    – DVK
    Jan 12, 2014 at 19:36
  • That distinction makes sense to me but I think is not what the question suggests - it suggests one form for both
    – mmmmmm
    Jan 12, 2014 at 19:39
  • re highlighting see these meta SO questions here and here
    – mmmmmm
    Jan 12, 2014 at 19:43

It is slightly complex as some types are actual acronyms with a given capitalisation used in formal specifications e.g. PDF EPUB whilst others are non official e.g. mobi which is short for Mobipocket and I don't think is officially defined.

Thus some should be simple words in capitals.

To be consistent I suppose we could make them all capitals unless there are examples that are not.

I do not think that using the . form in text is a good idea as nor all questions will refer to actual files.

  • 1
    Exactly. If you are talking about the EPUB format that does not necessarily imply that you mention an .epub file.
    – Anthon
    Jan 8, 2014 at 22:46
  • @Anthon - I think that when one talks about pure format it should be EPUB whereas about files, .epub. Usually it's easy to tell the context
    – DVK
    Jan 12, 2014 at 18:56

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