The now-common hashtag is a very loose form of structured data. While not always strictly used this way, hashtags are often used to describe a broader content category. Many web systems — Twitter being the most obvious example — convert hashtags into links that search data for other posts tagged with the same hashtag. While hashtags fail at being either controlled or hierarchically organized — two important attributes of structured data — they excel at helping information become more discoverable, which is the main purpose of structured data.