HTML 5 local Storage size limit for sub domains

HTML5's localStorage databases are size-limited. The standard sizes are 5 or 10 MB per domain. A limit of 5 MB per origin is recommended.

The following is stated −

User agents should guard against sites storing data under their origin's other
affiliated sites, e.g. storing up to the limit in,,, etc, circumventing the storage limit.

For size limit −

A mostly arbitrary limit of five megabytes per origin is suggested.
Implementation feedback is welcome and will be used to update this suggestion
in the future.