Facts are simple and facts are straight
Facts are lazy and facts are late

- Talking Heads, "Crosseyed and Painless", from Remain in Light, 1980

Facts can be simple, in which case their values must be expressed as simple content (except in the case of simple facts whose values are expressed as a ratio), and facts can be compound, in which case their value is made up from other simple and/or compound facts.

- XBRL Recommendation 2.1, section 1.4, "Terminology", 2005

(Sorry, couldn't resist that.) Most introductions to XBRL out there are aimed at financial people. They briefly touch on the what and why of the XML parts, but leave out the how, treating the technology part as a black box. Simple web searches turn up plenty of these introductions, so for those interested in a more technical, markup geek perspective, I wanted to give an overview of the better resources that I found. If you're coming at XBRL from an implementer's angle, it's certainly important to read the overviews aimed at the CFO and accountant crowd to learn what users do with this data and expect from the technology, but if you want to create or modify the technology you have to dig a little more for background.

• For an overview of XBRL's role in the standards world, Dale Waldt's XBRL: The Language of Finance and Accounting article in XML.com (part of a series titled "Standards Lowdown") answers key questions such as "What Is it?" and "Where does it come from?", so it's a good place to start.

• Although Wikipedia is aimed at a generalized audience, its XBRL entry packs a lot of technical detail and context into a fairly brief entry, so I strongly recommend that as one of the first things to look at.

• You wouldn't want to read all 165 pages of the actual XBRL Recommendation straight through, but as with any spec for a standard that you're interested in, it's worth reading the introductory part and skimming the rest to get an idea of what's there so that you know how it's organized when you need to look up something specific. I read about the first 20 pages, then my eyes glazed over when it started getting into detail about the more advanced XLink possibilities, so I skipped to the introductions of the XBRL Instances and XBRL Taxonomies sections.

• Lastly, there's a somewhat interactive tutorial at KPMG's website. (Don't even follow the link unless you're using Internet Explorer, which is obviously the first strike against the tutorial.) This tutorial has plenty of good information, but it's still a glorified PowerPoint presentation masquerading as a series of Interactive Course Module Rich User Experience Learning Management System Objects, or whatever the hell they're calling it. (I also question the expertise of any XML "experts" who don't understand the difference between elements and tags. And, don't be put off by the awful music with the title slides; it's only on the title slides.) Despite these annoyances, the KPMG tutorial lays out the elements and attributes that make up XBRL instances and taxonomies pretty well, and I took several pages of notes.

Do you know of any good introductions to XBRL aimed more at implementers than at accountants?