SPF Exists and Redirect -

i've been helping client email system , realised webmaster entered following spf record.

v=spf1 exists:%{i}._spf.somedomain.com redirect=_spf.somedomain.com ?all 

i've looked exists , redirect options. can tell these mean emails sent "from" domain come through authenticated spf?

the first part:

exists:%{i}._spf.somedomain.com 

says insert ip address, 1.2.3.4 example, giving:

exists:1.2.3.4._spf.somedomain.com 

which says, if dns 'a' lookup works, pass.

having both redirect , all kind of odd. redirect happens if else fails (which why should @ end of spf record), all never fails match.

if all wasn't there redirect:

redirect=_spf.somedomain.com 

would says go fetch spf record process it.