One of the key differences between ISL and $802\mathrm{.}1$q is the concept of a native VLAN. Which of the following is true about the native VLAN and its use in ISL and $802\mathrm{.}1$Q$?$

ISL does not encapsulate frames if they are a part of the native VLAN

$802\mathrm{.}1$Q does not tag $($add$)$ a trunking header to frames if they are a part of the native VLAN

ISL encapsulates frames for the native VLAN as if they were in reserved VLAN $999$

$802\mathrm{.}1$Q tags frames for the native VLAN as if they were in reserved VLAN $999$