Security Patch Level is supported below Marshmallow devices.

[crystal test]

Have tried to access and read both the system files "/system/build.prop" and   "/system/bin/getprop"  on v4.4.2,v5.0.2 devices, but not able to get any attribute related to security patch level(ro.build.version.security_patch). 

Also it is  mentioned that the  Samsung started showing Android security patch level for some Lollipop phones.When tried to access the system files on 5.1.1 samsung device, getting an attribute naming 'ro.build.version.security_patch'  with it associated value.

Please can I get any standard documentation whether security patch level feature is supported/or not supported for below Marshmellow devices except samsung devices.