Features pertaining to serial attribute-value pairs.

- numAttrValPairs: the number of attribute-value pairs the element has.
Regular: attribute, value completion
Parent: tag, attribute, value completion

- prevAttribute: the attribute preceding the attribute-value pair extracted for the table
- prevValue
- prevAttrVal

- attrIndex: the order in which the attribute extracted for the table appears in the element
- valIndex
- attrValIndex