MCS defines different variant types that are used in policies in different combinations.
MCS defines different variant types that are used in policies in different combinations.
Device specific
Convertible
Generic
Null
MCS uses the variant type to locate variants that are the best match for the device in use. The type also determines which of the values in the metadata of the Policy editor section are required, and therefore the error messages that you may see.
Most policy variants are device specific. They can be targeted at a particular device or device family. Text variants are an example of a targeted variant.
MCS searches the repository for a variant which is targeted at the device currently in use. If there is no match, MCS searches for variants targeted at categories, and then for variants that match the parent of the current device in the device tree. This search continues up the hierarchy until either a variant is found, or MCS reaches the root of the device tree.
Image variants may be treated as convertible variants. MCS routes the image through the Media Access Proxy (MAP), changing the file format and scaling it to fit the device in use.
Generic audio and image variants cater for variants that are not targeted, where the task of identifying images for particular devices at design time is very time consuming. MCS searches for a variant with properties that make it suitable. For audio variants, for example, the decision is based on how the audio data is encoded. With images, encoding, pixel depth, rendering and image size are all used.
Using a null variant value means that MCS will not search for variants matching other devices in the device hierarchy. It behaves as if no variant exists for this device
For example, setting an image variant for a PC device to 'Null' will prevent that image being used as fallback for a specific browser.
If you define a device specific or null type for a device, no other variants in the policy may be targeted at that device. If another device specific or null variant has the same target, you will see an error message.