#ifdef tag_1_1 tag_1_2 // first line
tag-1.1 or tag-1.2 is defined
#ifdef tag_2_1
(tag-1.1 or tag-1.2) and tag-2.1 is defined
#else
(tag-1.1 or tag-1.2) and not tag-2.1 is defined
#endif
tag-1.1 or tag-1.2 is defined
#endif
