Macromedia coldfusion 4.5-cfml language reference User Manual

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CFML Language Reference 
All of the above statements result in errors. As a general rule, never put pound signs 
around function arguments.
Pound signs in general expressions
Allaire recommends that pound signs be used only where necessary. The following 
example demonstrates the preferred method for referencing variables.
<CFSET SomeVar=Var1 + Max(Var2, 10 * Var3) + Var4>
It is a cleaner and more efficient method.
In contrast, note the following example, which uses pound signs unnecessarily:
<CFSET #SomeVar#=#Var1# + #Max(Var2, 10 * Var3)# + #Var4#>