CBA has info on Restricted Free Agency in Article 9, Section 2.
https://nflpaweb.blob.core.windows....eral/2011_Final_CBA_Searchable_Bookmarked.pdf
I'm reading this as follows:
1) Butler can only negotiate with another team up to 5 days prior to the draft. No one other than the Patriots can sign him after that point. The league and players have the option to extend that to a later date, but I'm not aware of that having happened; if it did happen, if he were signed to an offer sheet two days prior to the draft (or any time afterwards), the draft pick would be in 2018 instead of 2017.
2) If a team doesn't have a 1st round draft pick, they can't attempt to sign Butler.
3) In my previous post where I identified a "wink-wink" agreement between the Saints and Patriots? They have to tread carefully. Trades are allowed only if the player and NFLPA allows it, but there is supposed to be "no consideration" given between clubs for the decision to extend/not extend an offer sheet and to match/not match the offer sheets. Given it's the Pats and Saints, Goodell has to be salivating here.... Regardless of the above, if anyone makes an offer and the Patriots match, the Patriots cannot trade Butler to that team for a one year period.
4) Pats can't trade their first refusal rights. I never thought of that one....
5) Saints can't do a bait-and-switch, signing Butler to an offer sheet the Pats don't match and then immediately renegotiating. Have to wait a year for that. If the Pats match, there isn't an explicit similar restriction on their side.