Differences in assembly

Syntax

High and low bytes of an 16-bit value are acquired using the hi and lo functions, not the > and < operators.
Anonymous labels and local labels are not supported.
All labels defined in assembly are global.
Colons are required in label declarations.
Macros are inserted using the + operator.
Raw bytes are inserted using the Millfork array syntax, not with any pseudoopcode (like !byte, db or fcb)
Assembly blocks cannot contain definitions of constants or variables.
6502: To enforce zero-page addressing, wrap the argument in the lo function: lo(arg)
6502: To enforce absolute addressing, add a 16-bit zero to the argument: 0000 + arg
GameBoy: The $FF page loads/stores are written LDH (C),A, not LD ($FF00+C),A.
GameBoy: The loads/stores that postincrement/postdecrement HL write the HL register as HLI or HLD, not HL+ or HL-
Z80: Indexing using the index register uses the IX(1) syntax, not (IX+1) or 1(IX).
Z80: Most undocumented instructions are not supported. The only one supported is SLL.
6809: 0,X is assembled the same as ,X.
6502: To enforce direct-page addressing, prepend the argument with <: <arg.