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The mandatory type attribute provides information about the intent of the element. It helps improve processing. If the user agent does not recognize the specified type, (e.g., testing, experimental, and vendor specific types), it will be treated as unknown. (The user agent is any software or device that interprets WML.)
Permitted values:

accept Acknowledgment of acceptance
delete Delete item
help Request for help
options Options or additional operations
prev Backward navigation
reset Clearing or reset
X-*n or x-*n Experimental
vnd* Any mix of
upper or lower case
Vendor specific