Microsoft is to release the source code of part of its recently unveiled Silverlight 'Flash killer' plug-in. 

The Redmond giant unveiled Silverlight at the 2007 National Association of Broadcasters conference in April and released the beta version to the public yesterday.  

Specifically, Microsoft will open source the Dynamic Language Runtime (DLR) and the IronPython language.

"We are shipping IronPython and the DLR layer, which is a layer on top of the Common Language Runtime," said Jim Hugunin, a development leader for Microsoft's CLR.

"We are shipping both of these on CodePlex under the Microsoft Permissive License, which is the Berkeley Software Distribution-style Microsoft licence.

"And we are doing that partially to invite people to play with it, to give us a lot of feedback and to do interesting things with it. So it is very much in the source-available, do-with-it-what-you-want-to spirit."

The Microsoft Permissive License allows developers and users to view, modify and redistribute commercial and non-commercial source code without paying royalties to Microsoft.

Developers are then able to charge a license fee for any code they have added to the software.