CODE EDITOR:

Each code block will have its own UNDO/REDO and works when closed and re-opened.
Also added Low/Hi Literals: #<$literal/#>$literal
Also made sure inline byte tables push the program counter bytes in place.

Here is a useful routine for code block:

; ============================================

; Pre-populate Colour RAM ($D800) per row

; 25 rows x 40 columns - one colour per row,

; taken from a 25-entry table

; ============================================

        LDA #<$D800

        STA $F6              ; pointer lo

        LDA #>$D800

        STA $F7               ; pointer hi

        LDX #$00              ; X = row index, 0..24

ROWLOOP:

        LDA ROWCOLOURS,X

        STA $FC               ; this row's colour, stashed

        LDY #$00

COLLOOP:

        LDA $FC

        STA ($F6),Y

        INY

        CPY #40

        BNE COLLOOP

        ; advance pointer by 40 for next row

        CLC

        LDA $F6

        ADC #40

        STA $F6

        LDA $F7

        ADC #0

        STA $F7

        INX

        CPX #25

        BNE ROWLOOP

        JMP ROWSKIP           ; jump clean over the data table below

ROWCOLOURS:

        .byte $01,$0F,$0c,$0b,$06,$04,$0e,$05,$03,$0d

        .byte $01,$07,$0a,$08,$02,$09,$0b,$0c,$0f,$07

        .byte $03,$05,$0e,$06,$0c

ROWSKIP: