The procedure for drawing teams into groups for the 2018 World Cup has changed compared with 2014. (Source)
The principles are:
All teams will be allocated to pots 1 to 4 [...] The October 2017 edition of the FIFA/Coca-Cola World Ranking will be used to allocate all qualified teams to the four pots
no teams from the same confederation, with the exception of UEFA, which could have up to two teams in the same group, will be drawn into the same group.
How will the second constraint be enforced?
The 2014 draw allows for
Groups will be skipped to respect principle of geographic separation
If, hypothetically, Groups A-H have received their top seed and Groups A-G have also received their second seed as follows
A Russia Mexico B Brazil England C Belgium Spain D Germany Denmark E Poland Switzerland F Portugal Croatia G France Uruguay H Argentina
There is only one team left in pot 2 and that is Columbia. However they can't be placed in Group H as this violates the "no teams from the same confederation in the same group" rule.
Is the draw restarted, or is the draw "fudged" for example by moving Croatia to Group H and putting Columbia in group F. Or is Columbia place in Group A, and the first placable team from the next pot put into group H, and if this last rule, what if the very last team can't be placed while respecting the rules.
Are the detailed rules for the draw published anywhere?