.3.4 Sector-plane references (spref)
Sector-plane references or sprefs are used when lines refer to the features of planes in special or comparative ways. Sprefs are most often used to refer to the height (Z coordinate) or the texture of a plane. When using sprefs a set of sectors or planes has usually already been targeted. Sprefs do not have a data component. DED definitions of the spref types are listed below.

Flag { ID = “spref_none”; }
Flag { ID = “spref_my_floor”; Value = 0x1; }
Flag { ID = “spref_my_ceiling”; Value = 0x2; }
Flag { ID = “spref_original_floor”; Value = 0x3; }
Flag { ID = “spref_original_ceiling”; Value = 0x4; }
Flag { ID = “spref_current_floor”; Value = 0x5; }
Flag { ID = “spref_current_ceiling”; Value = 0x6; }
Flag { ID = “spref_highest_floor”; Value = 0x7; }
Flag { ID = “spref_highest_ceiling”; Value = 0x8; }
Flag { ID = “spref_lowest_floor”; Value = 0x9; }
Flag { ID = “spref_lowest_ceiling”; Value = 0xA; }
Flag { ID = “spref_next_highest_floor”; Value = 0xB; }
Flag { ID = “spref_next_highest_ceiling”; Value = 0xC; }
Flag { ID = “spref_next_lowest_floor”; Value = 0xD; }
Flag { ID = “spref_next_lowest_ceiling”; Value = 0xE; }
Flag { ID = “spref_min_bottom_texture”; Value = 0xF; }
Flag { ID = “spref_min_mid_texture”; Value = 0x10; }
Flag { ID = “spref_min_top_texture”; Value = 0x11; }
Flag { ID = “spref_max_bottom_texture”; Value = 0x12; }
Flag { ID = “spref_max_mid_texture”; Value = 0x13; }
Flag { ID = “spref_max_top_texture”; Value = 0x14; }
