Opera Core Concerns

As previously explained, Opera has a common foundation on every platform and release Opera ships on called the core, which consists of all the platform-independent bits and pieces that make the browser, such as the layout engine or ECMAScript engine.

The Opera Core, called Presto, is released internally at Opera at a schedule independent of any product releases, including Opera on desktop, Opera Mobile, Mini or Opera for devices. Normally, core makes three to four releases every year.

In the past, a developer could not directly determine which core version of Opera shipped with a particular release of Opera, but this changed with Opera 9.5 on desktop, where the User-Agent string changed.

In the past, a typical Opera User-Agent string would look like this:

Opera/8.54 (Windows NT 6.0; U; nl)

Starting with the previous release of Presto, the Opera core, we started identifying the version of Opera core in the User-Agent string:

Opera/9.62 (X11; Linux i686; U; en) Presto/2.1.1

The Presto components of the User-Agent string are on the format Presto/[Major version].[Minor version].[Maintenance version].

What to expect?

When developing against Opera, you can generally expect features to have the same level of support and issues, regardless of on which device. For instance, you can expect SVG, ECMAScript, CSS or DOM across all Opera releases shipping with a certain Presto version to behave the same.

This does not, however, mean that you should expect that all features from any given core release are available. Through a set of tweaks, a given shipment of an Opera product might disable or enable a certain feature. A good example of this is the web fonts feature for Presto 2.2.0 - it may be disabled for certain platforms, due to constraints on these platforms, such as low bandwith or low memory.

As for the maintenance versions: They are usually released a relatively short time after the minor version, and contain bug fixes that have surfaced since the release. In general, these versions will not affect any APIs or compatibility.

If you want to play with the latest and greatest Opera core, Opera 10 alpha 1 is shipping with the brand new Presto 2.2.0 release - an overview of the new features are to be found at dev.opera.com. A more detailed changelog can be found from our desktop team's announcment.