applies various validations - accumulates error messages in exc
applies various validations - accumulates error messages in exc
fail on first error, ignore other errors (rearranging conditions)
check children, return true if conform to content model
check children, return true if conform to content model
contentModel != null
check attributes, return true if md corresponds to attribute declarations in adecls.
set content model, enabling element validation
set meta data, enabling attribute validation
validate children and/or attributes of an element exceptions are created but not thrown.