California Assemblymember Toni Atkins introduces Gender Nondiscrimination Act | San Diego Gay and Lesbian News: "California non-discrimination laws already define 'gender' to include a person's gender identity (how they see themselves) and gender expression (how other people see them). AB 887 specifically enumerates gender identity and gender expression in order to simplify compliance with existing legal protections."
California law has long protected transgender people, and this change will make the statute clearer and more out front with the concept of transgender protection. The terms "gender identity" and "gender expresssion" are those ordinarily used in similar laws across the country.