Adding to Nick's reply in regards to Title 24 - Part 6 (California's State Building + M/E/P Codes are Title 24 - Part "_X_"):
California Energy Commission's Standards for Energy Conservation in New, Altered or Remodeled, & Additions in Residential and Non-Residential Occupancies cover the Building's Envelope (Framing, Insulation, Windows, etc.), M/E/P, and Appliances.
Anyone who has worked in the Construction Fields out here has at least heard of these Standards - and will be referred to in "Trade Slang" as "TITLE 24"
"a/b" Switching began in late 1970's for Commercial Installations.
By mid 1980's, Commercial Lighting included "Slave/Master" fixtures, Zones of upto 5,000 Sq. Ft. separately controlled via auto shutoffs (if all under one meter), multi level lighting controls ("a/b - c/d - e/f"), and use of energy saving Ballasts + Lamps (F40T12 Lamps rated for 34 Watts).
By mid 1990's, Daylit areas became included into "Dimming Scheme", lower TLP (Total Lighting Power) per Occupant Category, and more of an emphasis placed on automatic occupancy sensors for credits.
Also, 1 Family Residential installations became included into Standards (for Lighting, that is; - Mechanical and Building Envelope already involved since first adoption in 1970's).
Things took a gigantic change after the rolling blackouts situation.
The Compliance Standards at that time were the 1998 version. This version was quite different than the previous version of 1995 - but not as drammatic of change between 1998 and the currently used version - 2001 Nonresidential Compliance Manual.
The rolling blackouts modeled a Worse-Case-Scenario for the Energy Commission, and with this in mind - figured to revise many currently enacted Standards - both in the Residential and the Non-Residential Standards.
For more information regarding these Compliance Standards, check out: CEC-Title 24 Homepage
These energy conservation items are compiled into all Architectural & M/E/P/ Plansets.
Also per Business codes, if the Contractor is also doing the Installation, that Contractor may perform the designing and take responsibility upon the Documents as both designer and author (such as Design / Build).