captab

In Spectre User Manual the fixed/variable cap reported with the captab analysis is defined as follows,

1. fixed - stands for the device/wire parasitic capacitance

2. variable - stands for coupling and voltage-dependent capacitance

My question is,

1. What is "coupling" referring to? Is wire-wire parasitic "coupling" capacitance?

2. I assume the variable cap reports the maximum capacitance. How does spectre know the operating range for this information? Is it assumed to be the max allowed range based on the process?

Thanks much!