The feature that has been missing from Microsoft Edge for so long is just around the corner. We've known for a little while that extensions are due to make an appearance in an upcoming build of Windows 10, and ahead of this the first extension has made an appearance in the Windows Store.
Page Analyzer is an extension aimed at developers, so it's arrival in the Windows Store is a little odd. It's likely that extension support will be added in the next Windows 10 Redstone build, although there's no official timeline for this release at the moment.
While the appearance of the Page Analyzer extension will please those who have been waiting for Microsoft Edge to come of age, you'll have to wait a little longer to try it out. As noted by WindowsBlogItalia, although it is possible to install the extension, it is not possible to activate or use it at this stage.
Page Analyzer may not be the most exciting of extensions -- it appears to just give web developers advice about how their sites meet accessibility needs and comply with web standards -- it marks the end of a long wait. Also noteworthy is the fact that the extension offers support for ARM processors, indicating that it will be compatible with mobile devices as well.