Please explain extras in livecycle with an example. in terms of usage, form validations, best practices.Better if you can post a sample pdf along with it
There's this post as well, Adobe LiveCycle Designer Cookbooks by BR001: Custom Properties . Basically it is an area of a XFA form where you can put whatever content your system needs. I tend to use the <desc> element instead as this shows up on the Info tab in Designer, though if you are importing a schema with annotations these will also be loaded under the <desc> element so you may want to keep them separate. The <desc> and <extras> can be access the same way and there is an example in the blog above.