ref: b9d96c7baee1327e46d8e69e7d2caf119ae95bb4
dir: /sys/src/libcontrol/group.h/
typedef struct Group Group;
struct Group {
Control;
int lastbut;
int border;
int mansize; /* size was set manually */
int separation;
int selected;
int lastkid;
CImage *bordercolor;
CImage *image;
int nkids;
Control **kids; /* mallocated */
Rectangle *separators; /* mallocated */
int nseparators;
};