ZX Spectrum & Timex special / advanced screen modes

Deep dive on the special / advanced graphics display modes of the ZX Spectrum 128/+2/+3 and the Timex TC2048 / TS2068 — everything beyond the plain 256×192 screen with 8×8 attributes. Use this WHENEVER the user wants Timex hi-res 512×192 monochrome, Timex hi-colour 8×1 attributes (one attribute per pixel row, no vertical colour clash), the Timex second display file, the ZX Spectrum 128K shadow / second screen and double-buffering via the 0x7FFD paging port, software multicolour (raster-synced attribute changes, Bifrost* / Nirvana / Nirvana+ engines), gigascreen / flicker colour mixing, interlacing for extra vertical resolution, or ULAplus 64-colour palette enhancement — i…