The installation directory ($INSTDIR is modifiable using StrCpy, ReadRegStr, ReadINIStr, etc. - This could be used, for example, in the .onInit function to do a more advanced detection of install location).
\e{$OUTDIR}
The current output directory (set implicitly via SetOutPath or explicitly via StrCpy, ReadRegStr, ReadINIStr, etc)
User variables (set via StrCpy, ReadRegStr, ReadINIStr, etc, and use like any other variable). It is recommended (but not required) that you use $R1-$R9 as local registers, and $0-$9 as global values. Note that any function that lets you specify one of these variables as an output, can use $INSTDIR or $OUTDIR as well (but has different implications).
\e{$CMDLINE}
The command line of the installer. The format of the command line can be one of the following:
\b For parsing out the PARAMETER portion, see GetParameters on the utility functions page. It's worth noting that if /D= is specified on the command line (to override the install directory), it won't be in $CMDLINE.
\e{$LANGUAGE}
The identifier of the language that is currently used. For example, English is 1033. You can change this variable in .onInit.
\H{var2} Constant Variables used in Instructions and InstallDir
\e{$PROGRAMFILES}
The program files directory (usually C:\\Program Files but detected at runtime).
\e{$DESKTOP}
The windows desktop directory (usually C:\\windows\\desktop but detected at runtime). The context of this variable (All Users or Current user) depends on the SetShellVarContext setting. The default is the current user.
\e{$EXEDIR}
The location of the installer executable. (technically you can modify this variable, but it is probably not a good idea)
The windows directory (usually C:\\windows or C:\\winnt but detected at runtime)
\e{$SYSDIR}
The windows system directory (usually C:\\windows\\system or C:\\winnt\\system32 but detected at runtime)
\e{$TEMP}
The system temporary directory (usually C:\\windows\\temp but detected at runtime)
\e{$STARTMENU}
The start menu folder (useful in adding start menu items using CreateShortCut)
\e{$SMPROGRAMS}
The start menu programs folder (use this whenever you want $STARTMENU\\Programs). The context of this variable (All Users or Current user) depends on the SetShellVarContext setting. The default is the current user.
\e{$SMSTARTUP}
The start menu programs / startup folder. The context of this variable (All Users or Current user) depends on the SetShellVarContext setting. The default is the current user.
\e{$QUICKLAUNCH}
The quick launch folder for IE4 active desktop and above. If quick launch is not available, simply returns the same as $TEMP. The context of this variable (All Users or Current user) depends on the SetShellVarContext setting. The default is the current user.
\e{$HWNDPARENT}
The decimal HWND of the parent window.
\e{$$}
Use to represent $.
\H{var3} Variables used Strings
\e{$\\r}
Use to represent a carriage return (\\r).
\e{$\\n}
Use to represent a newline (\\n).
\e{$\{SYMBOL\}}
Where SYMBOL is the name of something globally defined, this will be replaced with the value of that symbol. If the symbol is not defined, no replace occurs (i.e. if $\{POOP\} is encountered, and POOP is not defined, $\{POOP\} is output).
