What does this SQL command accomplish?

ALTER TABLE PRODUCTS

ADD CHECK $($SIZE IN $(\text{'}$S$\text{'},\text{'}$M$\text{'},\text{'}$L$\text{'},\text{'}$XL$\text{'},\text{'}$XXL$\text{'}))$;

updates all values in the SIZE column

adds a parent$-$child constraint to the PRODUCTS table

establishes a foreign key for the PRODUCTS table

establishes legal values for the SIZE column