Evaluates a conditional statement.
 if <conditional statement> ({&&,&} <conditional statement>) <commands>
The commands following the if statement are executed if the conditional statement(s) evaluate true; if you want branch control in which a command executes if a conditional statement is false, use notif.
The conditions can compare numerical values, else you can employ fchk.
& and && are logical 'ands', and are equivalent to one another.

   <numerical variable> {>,<,=,>=,<=,==,!=,<>} <numerical variable>
   - or -
   fchk <character string>

   <,>,=,>=,<= should already be known to you.
   == and = are identical, as are != and <>.
   As for fchk, it returns true when the image whose name corresponds to the character string is being used.

    if %0=1 quakex 2 (basic form)
    if %0=1 && %2=5 end (multiple conditions)
    if %0=2 mov %1,1:skip 2 (append additional commands with :)
    notif %0=1 quakex 2 (in C, this would be if(%0!=1) quakex 2;)