| 254 | | @defmac defcustom option default doc [keyword value]@dots{} |
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| 255 | | Declare @var{option} as a customizable user option variable. Do not |
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| 256 | | quote @var{option}. The argument @var{doc} specifies the documentation |
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| 257 | | string for the variable. There is no need to start it with a @samp{*} |
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| 258 | | because @code{defcustom} automatically marks @var{option} as a |
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| 259 | | @dfn{user option} (@pxref{Defining Variables}). |
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| 260 | | |
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| 261 | | If @var{option} is void, @code{defcustom} initializes it to |
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| 262 | | @var{default}. @var{default} should be an expression to compute the |
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| 263 | | value; be careful in writing it, because it can be evaluated on more |
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| 264 | | than one occasion. You should normally avoid using backquotes in |
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| 265 | | @var{default} because they are not expanded when editing the value, |
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| 266 | | causing list values to appear to have the wrong structure. |
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| | 254 | @defmac defcustom option standard doc [keyword value]@dots{} |
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| | 255 | This construct declares @var{option} as a customizable user option |
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| | 256 | variable. You should not quote @var{option}. The argument @var{doc} |
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| | 257 | specifies the documentation string for the variable. There is no need |
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| | 258 | to start it with a @samp{*}, because @code{defcustom} automatically |
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| | 259 | marks @var{option} as a @dfn{user option} (@pxref{Defining |
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| | 260 | Variables}). |
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| | 261 | |
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| | 262 | The argument @var{standard} is an expression that specifies the |
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| | 263 | standard value for @var{option}. Evaluating the @code{defcustom} form |
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| | 264 | evaluates @var{standard}, but does not necessarily install the |
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| | 265 | standard value. If @var{option} already has a default value, |
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| | 266 | @code{defcustom} does not change it. If the user has saved a |
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| | 267 | customization for @var{option}, @code{defcustom} installs the user's |
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| | 268 | customized value as @var{option}'s default value. If neither of those |
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| | 269 | cases applies, @code{defcustom} installs the result of evaluating |
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| | 270 | @var{standard} as the default value. |
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| | 271 | |
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| | 272 | The expression @var{standard} can be evaluated at various other times, |
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| | 273 | too---whenever the customization facility needs to know @var{option}'s |
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| | 274 | standard value. So be sure to use an expression which is harmless to |
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| | 275 | evaluate at any time. We recommend avoiding backquotes in |
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| | 276 | @var{standard}, because they are not expanded when editing the value, |
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| | 277 | so list values will appear to have the wrong structure. |
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