From SNPedia

genoset criteria syntax currently supports the following

rs1234(A;T)

True if at both alleles are observed.

rs1234(T;T)

True if only the T allele is observed.

rs1234(T)

True if at least one T allele is observed.

and(rs1234(A;T),rs1235(A;T))

Example: gs102/criteria

or(rs1234(A;T),rs1235(A;T))

Example: gs101/criteria

atleast(2,rs1234(A;T),rs1235(A;T),rs1236(A;T))

Example: gs111/criteria

not(rs1234(T;T))
not(rs1234(T;T),rs1235(T;T))

True if all elements are False

You can also refer to other genosets. Example: gs1011/criteria

[edit] Comments

Two types of comments are allowed.

# this 
### syntax is visible and allows hyperlinks
lines must begin with a space

<!-- comments --> syntax is also allowed, but will not show until someone is editing the criteria

Example: gs1013/criteria