Welcome to the Platform Preview
The Platform Preview is an early look at the Internet Explorer platform so some features are incomplete, some may change, and some may be added. To learn more about this preview of the Web Platform, please see the Internet Explorer 10 Developer Guide. These release notes list new features available in the latest Platform Preview and known issues with those features. To report issues, and provide feedback please click on Report Issue and click Send Feedback.
What's New in Internet Explorer 10 Platform Preview 1
Internet Explorer 10 Platform Preview 1 is the first public preview of the IE10 web platform. In this release, we are showcasing support for CSS3 Flexbox, CSS3 Grid Alignment, CSS3 Multi-column, CSS3 Gradients on background-images and ECMAScript5 Strict Mode.

System Requirements
The Internet Explorer Platform Preview requires Windows 7 (x86 or x64) Operating System. Platform Preview 4 and later require updates to be installed on Windows 7 systems, after which your computer will require a restart. The updates support Platform Preview graphics, media, and printing functionality. The Platform Preview is designed to install these prerequisites automatically. However, if the Platform Preview encounters an error while installing the prerequisites, you can install them manually prior to installing the Platform Preview. To do so, follow the steps on the Install Instructions page.

Platform Preview Compatibility List
The platform preview ships with a pre-defined compatibility view list that is designed to mitigate website compatibility problems you may encounter while using the platform preview. Although Internet Explorer constantly updates its compatibility view list, the list consumed by the platform preview is static. To use the most up-to-date version of the compatibility view list with the Platform Preview, please follow these steps:
Download the latest compatibility view list and store it in: C:\Program Files\Internet Explorer Platform Preview\iecompatdata.xml
Change this reg key to 0: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\BrowserEmulation\PPB\IECompatVersionLow
Close your platform preview window and reopen it.
The platform preview will pick up the new CV list once you restart the application.

Breaking Changes
Event object's 'trusted' property
In recent changes to the W3C DOM Level 3 Events specification's Last Call feedback, the working group elected to change the 'trusted' property to 'isTrusted' to match the property of the same name and semantics in Mozilla browsers. IE's implementation of this property has been adjusted to match.
DOM Programmability
Invoking cached DOM functions without using the dot (.) notation and without using call/apply/bind now throws script errors. The previously supported legacy function invocation pattern has been removed for better interoperability and standards support:
var g = document.getElementById; g(‘test’); // Now throws an exception
Enumeration of DOM objects previously only included properties and event handlers. With IE9 and IE10 standards mode, enumeration now includes functions as well. Support for invoking collection objects as functions (rather than array-indexing): document.images(0) has been removed from the following collection objects: HTMLFormElement, window.frames, document.frames, NodeList.
HTCs / VBScript
HTML Components (HTC) and VBScript code when used inside of an IE9 or IE10 standards mode page are no longer executed in compatibility view. Consequently, DOM APIs used by the HTC or VBScript code now behave according to the IE standards mode version of the same APIs.
DOM Properties in Attributes Collection
Properties set on DOM objects no longer appear in the attributes collection (NamedNodeMap) and vice versa in IE9 or IE10 standards mode. This change also aligns IE’s programmability model with current standards and interoperability.

Platform Preview Known Issues
Platform Preview may crash IE8
Running Platform Preview builds side by side with IE8 can occasionally cause crashes or corrupted networking stacks in IE8. Closing the Platform Preview (which appears as the iepreview.exe process in Task Manager) will resolve all such issues in IE8.
Platform Preview shows an error dialog when IE8 is running
When IE8 and the Platform Preview are running simultaneously, a dialog may appear in the Platform Preview that says "The specified procedure could not be found." To avoid this issue, close either IE8 or the Platform Preview.
Platform Preview Build opens links to *.EXE files as text
Description: When you click a link to an executable (.EXE) in the Platform Preview, it will open in the Platform Preview as a text file. To work around this issue: Right click the link and choose "Save Target As..." to save the linked file to your machine, after which you may run it. For more information see connect issue 556100.
Downloads initiated by script do not function
There is no Information Bar (aka Gold Bar) in Platform Preview. As a result, downloads initiated by script will not function. Files can be downloaded using the “Save Target As…” in the right-click context menu, by clicking on hyperlinks to files, and by typing a download URL in the Open dialog (Ctrl+O).
Upgrading the Platform Preview Build turns the taskbar pinned icon into a blank page icon
When a user upgrades from one version of the Platform Preview Build to the next, the taskbar pinned icon to turns into a blank page icon. As a workaround you can right click the icon on the taskbar and select "Unpin this program from taskbar". Open the Start Menu, right click the newly installed Internet Explorer Platform Preview under All Programs, and click "Pin to Taskbar". For more information see connect issue 556106.

CSS Grid and CSS Flexbox do not currently support anonymous text blocks
A temporary workaround is to wrap such blocks with an explicit element.
The CSS calc() function is not currently supported for CSS3 multicolumn properties
Layering is not currently supported in CSS3 Grid
Absolutely positioned elements contained within a multicolumn element may be positioned incorrectly if they are encountered after the multicolumn fragment in which they should be positioned
Borders may be drawn outside of the border box when specified on a CSS Grid item

CSS3 Gradients Color Interpolation
CSS3 gradients in PPB1 are interpolated in a non-premultiplied alpha color space. Due to this, gradients containing color stops with differing alpha values may appear to be less attractive than expected. CSS3 gradients will be interpolated in a premultiplied alpha color space in a future IE10 platform preview.
CSS3 Gradients on list-style-image and generated content
CSS3 gradients in PPB1 only works for background-image. Support for list-style-image and generated content will come in a future IE10 platform preview.

D2D Rendering
In rare circumstances, the IE Platform Preview may render Web page content incorrectly or slowly on some older graphics cards. You may see page content garbled or page scrolling may be slow. Though this issue is known and being fixed, we would still like to hear about your specific issues. Please use the ‘Report an Issue’ feature in the Platform Preview to bring this issue to our attention. Be sure to include the output file created by running IE Diagnostics in the Platform Preview’s Report Issue menu. To work around the issue while running the Platform Preview, please download and run the "Force D2D Software Mode" registry file and restart the Platform Preview. To switch back to graphics card based rendering again, please download and run the "Force D2D Hardware Mode" registry file and restart the Platform Preview.

SVG Performance
In general, performance with “normal” SVG files is good. However, performance work on large or complex SVG files is not yet complete. You will see this most with CAD- or GIS-generated SVG images.

SVG Text
In SVG documents, highlighting and selecting text content may not work correctly in some scenarios
Adding properties from CSS tab doesn't update the style and trace style tab
Style properties added in the 'CSS' view of the developer tools are not included in the CSS tracing displayed in the 'Style' or 'Trace Styles' sections of the 'HTML' view. More Information
Right click context menu for SVG is missing "View Source"
The right-click context menu on SVG content no longer contains the "View Source" option. More Information The source code can still be obtained via the Developer Toolbar (F12) --> View --> Source --> Original
CSS calc() does not support unary operators
Unary operators do not work in the calc function. For example calc(-2px + +5px) will not work though calc(2px + 5px) does work. More Information

Canvas drawImage
If the Canvas element’s 2D context’s drawImage() method is called with an HTMLVideoElement, the origin-clean flag will be set to false.
KeyboardEvent's key property and dead keys
For some international keyboard layouts, the 'key' and 'char' properties for "dead keys" (virtual combining characters) will not be reported correctly [will be limited to the alpha-numeric range], or may be reported as "Unidentified"/null for 'key' and 'char' respectively, when accessed through a keydown or keyup event handler. For example, the "é" keydown and keyup events following the "combining acute accent" dead key on a Spanish keyboard layout will be reported as "e". (The keypress event will correctly return the value "é" from the 'key' property, however.) IE will also report "Unidentified" rather than "DeadEacute" for the combining acute accent key in this example.
removeAttribute(‘value’) on input elements
Using the removeAttribute(‘value’ ) method on an input element will fail to remove the value attribute.