This is Pg 25-26 of the rule book. Bold/Underlined text answers question about where it's found.
B. Two Striper:
1. Cannot have more than 3 two stripe players on the field
of play at any one time.
2. Can only be a lineman in a down position, 3 or 4 point
stance.
3. Cannot be on the kick-off or kick-return team.
Offense
1. Must play on the interior offensive line and may never
be in a position to be eligible for a pass. Note: On an
unbalanced line, the tackle becomes an end if
uncovered making him illegal.
2. Will be allowed in the backfield to kick extra points or
field goals only. The kick must be a declared, a fumble
or fake will be declared a dead ball. If the kick is blocked
and remains behind the line of scrimmage, a Two Striper
may advance the ball.
3. Two stripers cannot advance the ball in a designed play
but may advance after the recovery of a DEFENSIVELY
CAUSED fumble.
Defense
1. Must play on the defensive line and will not line up any
wider than head-up with the tight end’s normal position
whether a tight end is lined up on that side or not.
2. Will be allowed to return a fumble or pass interception.