ARM VERSION 1.2 - Manual (Page 86)

Assembler Reference
3-8 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
3.2 Format of source lines
The general form of source lines in an ARM assembly language module is:
{symbol} {instruction|directive|pseudo-instruction} {;comment}
All three sections of the source line are optional.
Instructions cannot start in the first column. They must be preceded by white space even
if there is no preceding symbol.
You can write directives in all upper case, as in this manual. Alternatively, you can write
directives in all lower case. You must not write a directive in mixed upper and lower
case.
You can use blank lines to make your code more readable.
symbol is usually a label (see Labels on page 3-15). In instructions and
pseudo-instructions it is always a label. In some directives it is a symbol for a variable
or a constant. The description of the directive makes this clear in each case.
symbol must begin in the first column and cannot contain any whitespace character such
as a space or a tab (see Symbol naming rules on page 3-12).