<div style="white-space:pre-wrap">The distinction is still mystifying after reading that section. If I read it right, a word is considered a "common word" if it's a dictionary headword in whatever dictionary happens to be on the bookshelf. Thus, because "ID" has an entry in that dictionary, it must be spelled "Id", but "IO" must be left alone apparently because it wasn't in the dictionary of choice (or, wasn't given in "closed form" in that dictionary) at the time the API authors looked it up. But I can tell you for certain that "UI" is now included in the Oxford English Dictionary (as of 2012 draft additions), while "IO" is listed as "I/O".</div><br><div class="gmail_quote"><div dir="ltr">On Fri, Feb 12, 2016 at 12:29 PM Carlos Parada <<a href="mailto:carlosparada@mac.com">carlosparada@mac.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Acronyms vs. abbreviations is my own way of understanding it, but the actual .NET guidelines list “Id" under “Compound Words and Common Terms”. The guidelines are here:<br>
<br>
<a href="https://msdn.microsoft.com/en-us/library/ms229043(v=vs.110).aspx" rel="noreferrer" target="_blank">https://msdn.microsoft.com/en-us/library/ms229043(v=vs.110).aspx</a><br>
<br>
“Ok” and “Pi” are other ones listed under “Compound Words and Common Terms".<br>
<br>
— Carlos Parada<br>
<br>
<br>
> On Feb 12, 2016, at 10:11 AM, Xiaodi Wu via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:<br>
><br>
> Oy. Distinguishing acronyms and abbreviations: this can't lead to<br>
> anything good. Reminds me of the seemingly endless attempt at<br>
> distinguishing <abbr> from <acronym> in HTML (until the standard<br>
> standardized on the former). For one, there's no agreed-upon<br>
> definition of the distinction between the two:<br>
> <a href="http://data.grammarbook.com/blog/abbreviations/abbreviations-acronyms-and-initialisms-revisited/" rel="noreferrer" target="_blank">http://data.grammarbook.com/blog/abbreviations/abbreviations-acronyms-and-initialisms-revisited/</a><br>
><br>
> If we use a commonly used distinction--that acronyms are "pronounced<br>
> as words" but abbreviations are not--neither "ID" nor "IO" are<br>
> pronounced "as words."<br>
><br>
><br>
> On Fri, Feb 12, 2016 at 12:04 PM, Carlos Parada <<a href="mailto:carlosparada@mac.com" target="_blank">carlosparada@mac.com</a>> wrote:<br>
>> I’ve used the .NET frameworks and conventions extensibly and while some of them didn’t look quite right initially, they grew up on me, and now I prefer them.<br>
>><br>
>> They do seem to use uppercase for two letter acronyms, but not for abbreviations though. When I started doing .NET I was so used to typing ID (as in identifier), but their convention is to type Id, as in CustomerId, or idForObject. It makes sense, just as you would use Ptr for Pointer, or Int for Integer.<br>
>><br>
>> — Carlos Parada<br>
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<br>
</blockquote></div>