Where did you see this notation?
Penal Code 667.5(c) lists the felonies that are considered violent felonies in California. There is no subsection "z."
A defendant convicted of one of these offense must serve 85% of any prison sentence imposed, instead of half of the time, which is the case with most other felonies.
Conviction of a 667.5(c) violent offense can also be charged in any future felony prosecution as a "strike" under the Three Strikes law, which substantially increases the punishment.
As indicaed there is no "z" in California Penal Code Section 667.5 (c) . Subsection (c) lists 23 offenses which are considered to be "violent felonies". First step in ascertaining charge and severity is to determine wether complaint or information alleges that new offense is a strike or whether it alleges that the defendant has suffered a prior strike. Sentencing is very complicated in these matters. There are whole books written on the topics.