*
* The syntax parsed from 's' takes the form "header[start..end]" where
* 'header' is the name of an NXM field and 'start' and 'end' are (inclusive)
* bit indexes. "..end" may be omitted to indicate a single bit. "start..end"
* may both be omitted (the [] are still required) to indicate an entire
* field. */
*
* The syntax parsed from 's' takes the form "header[start..end]" where
* 'header' is the name of an NXM field and 'start' and 'end' are (inclusive)
* bit indexes. "..end" may be omitted to indicate a single bit. "start..end"
* may both be omitted (the [] are still required) to indicate an entire
* field. */