Facebook opens up its markup language (sort of)
Facebook on Tuesday announced that it has made the Facebook Markup Language extensible, enabling developers outside of Facebook to create custom tags.
For example, the iLike application developers have provided an iLike tag that shows favorite songs and playlists.
Initially, FBML included only tags that Facebook created. Today, we're excited to announce a new feature called custom tags. With custom tags, any developer can create new FBML tags. Developers can use these tags in their own applications, or they can share their custom tags with the entire Facebook developer community as prebuilt FBML components.
This is a great step forward, but it's also a highly limited one, as ReadWriteWeb points out. To be highly reusable and, hence, more useful, Facebook should consider exposing its markup code to developers so it can be "more easily altered for reuse in different ways by different apps."
Exactly. This is one of the cardinal virtues of open source: code reuse. By allowing development of custom tags, Facebook has taken a step toward openness, but not the one that developers require to be efficient with their code.
Mike Vernal, a member of Facebook's Platform Engineering Team, tells Web 2.0 Journal that "our goal with Platform has been to allow applications anywhere to become more social by leveraging the power of Facebook," but this becomes doubly difficult if the platform is closed.
Sure, some companies can pull off a widely used, mostly closed platform. Microsoft certainly has. But in the age of the Internet, it's much easier to accomplish platform adoption through transparency and open code, making it harder to justify keeping the Facebook platform closed.
Matt Asay brings a decade of in-the-trenches open-source business and legal experience to The Open Road, with an emphasis on emerging open-source business strategies and opportunities. Matt is vice president of business development at Alfresco, a company that develops open-source software for content management. He is a member of the CNET Blog Network and is not an employee of CNET. Disclosure. You can follow Matt on Twitter @mjasay. 
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"You can retrieve your application's custom tags using fbml.getCustomTags. If a tag is public, any application can fetch the tag's source FBML by calling fbml.getCustomTags. Don't register public tags with the expectation that the source FBML won't be available to other developers."
This means anybody can get the source code for public (shared) custom tags.