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(Warnings): New node, and subnodes.
(Fringes): New node.
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@ -15,6 +15,7 @@ that Emacs presents to the user.
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* Forcing Redisplay:: Forcing redisplay.
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* Truncation:: Folding or wrapping long text lines.
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* The Echo Area:: Where messages are displayed.
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* Warnings:: Displaying warning messages for the user.
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* Invisible Text:: Hiding part of the buffer text.
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* Selective Display:: Hiding part of the buffer text (the old way).
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* Overlay Arrow:: Display of an arrow to indicate position.
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@ -23,6 +24,7 @@ that Emacs presents to the user.
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* Width:: How wide a character or string is on the screen.
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* Faces:: A face defines a graphics style for text characters:
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font, colors, etc.
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* Fringes:: Controlling window fringes.
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* Display Property:: Enabling special display features.
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* Images:: Displaying images in Emacs buffers.
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* Blinking:: How Emacs shows the matching open parenthesis.
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@ -111,10 +113,9 @@ the rightmost column indicates a line that ``wraps'' onto the next line,
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which is also called @dfn{continuing} the line. (The display table can
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specify alternative indicators; see @ref{Display Tables}.)
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@cindex fringes, and line continuation/truncation indicators
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On a windowed display, the @samp{$} and @samp{\} indicators are
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replaced with graphics bitmaps displayed on the thin areas right near
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the window edges, called the @dfn{fringes}.
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replaced with graphics bitmaps displayed in the window fringes
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(@pxref{Fringes}).
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Note that continuation is different from filling; continuation happens
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on the screen only, not in the buffer contents, and it breaks a line
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@ -327,6 +328,194 @@ sequence are echoed immediately.)
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If the value is zero, then command input is not echoed.
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@end defvar
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@node Warnings
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@section Reporting Warnings
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@cindex warnings
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@dfn{Warnings} are a facility for a program to inform the user of a
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possible problem, but continue running.
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@menu
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* Warning Basics:: Warnings concepts and functions to report them.
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* Warning Variables:: Variables programs bind to customize their warnings.
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* Warning Options:: Variables users set to control display of warnings.
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@end menu
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@node Warning Basics
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@subsection Warning Basics
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@cindex severity level
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Every warning has a textual message, which explains the problem for
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the user, and a @dfn{severity level} which is a symbol. Here are the
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possible severity levels, in order of decreasing severity, and their
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meanings:
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@table @code
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@item :emergency
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A problem that will seriously impair Emacs operation soon
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if you do not attend to it promptly.
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@item :error
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A report of data or circumstances that are inherently wrong.
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@item :warning
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A report of data or circumstances that are not inherently wrong, but
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raise suspicion of a possible problem.
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@item :debug
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A report of information that may be useful if you are debugging.
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@end table
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When your program encounters invalid input data, it can either
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signal a Lisp error by calling @code{error} or @code{signal} or report
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a warning with severity @code{:error}. Signaling a Lisp error is the
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easiest thing to do, but it means the program cannot continue
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processing. If you want to take the trouble to implement a way to
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continue processing despite the bad data, then reporting a warning of
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severity @code{:error} is the right way to inform the user of the
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problem. For instance, the Emacs Lisp byte compiler can report an
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error that way and continue compiling other functions. (If the
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program signals a Lisp error and then handles it with
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@code{condition-case}, the user won't see the error message; it could
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show the message to the user by reporting it as a warning.)
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@cinedex warning type
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Each warning has a @dfn{warning type} to classify it. The type is a
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list of symbols. The first symbol should be the custom group that you
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use for the program's user options. For example, byte compiler
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warnings use the warning type @code{(bytecomp)}. You can also
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subcategorize the warnings, if you wish, by using more symbols in the
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list.
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@defun display-warning type message &optional level buffer-name
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This function reports a warning, using @var{message} as the message
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and @var{type} as the warning type. @var{level} should be the
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severity level, with @code{:warning} being the default.
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@var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
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for logging the warning. By default, it is @samp{*Warnings*}.
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@end defun
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@defun lwarn type level message &rest args
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This function reports a warning using the value of @code{(format
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@var{message} @var{args}...)} as the message. In other respects it is
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equivalent to @code{display-warning}.
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@end defun
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@defun warn message &rest args
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This function reports a warning using the value of @code{(format
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@var{message} @var{args}...)} as the message, @code{(emacs)} as the
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type, and @code{:warning} as the severity level. It exists for
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compatibility only; we recommend not using it, because you should
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specify a specific warning type.
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@end defun
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@node Warning Variables
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@subsection Warning Variables
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Programs can customize how their warnings appear by binding
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the variables described in this section.
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@defvar warning-levels
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This list defines the meaning and severity order of the warning
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severity levels. Each element defines one severity level,
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and they are arranged in order of decreasing severity.
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Each element has the form @code{(@var{level} @var{string}
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@var{function})}, where @var{level} is the severity level it defines.
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@var{string} specifies the textual description of this level.
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@var{string} should use @samp{%s} to specify where to put the warning
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type information, or it can omit the @samp{%s} so as not to include
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that information.
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The optional @var{function}, if non-@code{nil}, is a function to call
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with no arguments, to get the user's attention.
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Normally you should not change the value of this variable.
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@end defvar
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@defvar warning-prefix-function
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If non-@code{nil}, te value is a function to generate prefix text for
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warnings. Programs can bind the variable to a suitable function.
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@code{display-warning} calls this function with the warnings buffer
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current, and the function can insert text in it. That text becomes
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the beginning of the warning message.
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The function is called with two arguments, the severity level and its
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entry in @code{warning-levels}. It should return a list to use as the
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entry (this value need not be an actual member of
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@code{warning-levels}). By constructing this value, the function to
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change the severity of the warning, or specify different handling for
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a given severity level.
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If the variable's value is @code{nil} then there is no function
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to call.
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@end defvar
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@defvar warning-series
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Programs can bind this variable to @code{t} to say that the next
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warning should begin a series. When several warnings form a series,
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that means to leave point on the first warning of the series, rather
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than keep move it for each warning so that it appears on the last one.
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The series ends when the local binding is unbound and
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@code{warning-series} becomes @code{nil} again.
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The value can also be a symbol with a function definition. That is
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equivalent to @code{t}, except that the next warning will also call
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the function with no arguments with the warnings buffer current. The
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function can insert text which will serve as a header for the series
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of warnings.
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Once a series has begun, the value is a marker which points to the
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buffer position in the warnings buffer of the start of the series.
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The variable's normal value is @code{nil}, which means to handle
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each warning separately.
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@end defvar
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@defvar warning-fill-prefix
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When this variable is non-@code{nil}, it specifies a fill prefix to
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use for filling each warning's text.
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@end defvar
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@defvar warning-type-format
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This variable specifies the format for displaying the warning type
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in the warning message. The result of formatting the type this way
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gets included in the message under the control of the string in the
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entry in @code{warning-levels}. The default value is @code{" (%s)"}.
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If you bind it to @code{""} then the warning type won't appear at
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all.
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@end defvar
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@node Warning Options
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@subsection Warning Options
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These variables are used by users to control what happens
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when a Lisp program reports a warning.
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@defopt warning-minimum-level
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This user option specifies the minimum severity level that should be
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shown immediately to the user. The default is @code{:warning}, which
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means to immediately display all warnings except @code{:debug}
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warnings.
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@end defopt
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@defopt warning-minimum-log-level
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This user option specifies the minimum severity level that should be
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logged in the warnings buffer. The default is @code{:warning}, which
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means to log all warnings except @code{:debug} warnings.
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@end defopt
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@defopt warning-suppress-types
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This list specifies which warning types should not be displayed
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immediately for the user. Each element of the list should be a list
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of symbols. If its elements match the first elements in a warning
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type, then that warning is not displayed immediately.
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@end defopt
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@defopt warning-suppress-log-types
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This list specifies which warning types should not be logged in the
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warnings buffer. Each element of the list should be a list of
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symbols. If it matches the first few elements in a warning type, then
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that warning is not logged.
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@end defopt
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@node Invisible Text
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@section Invisible Text
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@ -572,7 +761,6 @@ interface to debuggers, the overlay arrow indicates the line of code
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about to be executed.
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@defvar overlay-arrow-string
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@cindex fringe, and overlay arrow display
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This variable holds the string to display to call attention to a
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particular line, or @code{nil} if the arrow feature is not in use.
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On a graphical display the contents of the string are ignored; instead a
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@ -2287,6 +2475,54 @@ Then, the font specifications for all but Chinese GB2312 characters have
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Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
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field.
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@node Fringes
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@section Fringes
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@cindex Fringes
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The @dfn{fringes} of a window are thin vertical strips down the
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sides that are used for displaying bitmaps that indicate truncation,
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continuation, and horizontal scrolling, the overlay arrow. The
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fringes normally appear between the display margins and the window
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text, but you can put them outside the display margins for a specific
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buffer by setting @code{fringes-outside-margins} buffer-locally to a
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non-@code{nil} value.
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@defvar fringes-outside-margins
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If the value is non-@code{nil}, the frames appear outside
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the display margins.
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@end defvar
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@defvar left-fringe-width
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This variable, if non-@code{nil}, specifies the width of the left
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fringe in pixels.
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@end defvar
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@defvar right-fringe-width
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This variable, if non-@code{nil}, specifies the width of the right
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fringe in pixels.
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@end defvar
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The values of these variables take effect when you display the
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buffer in a window. If you change them while the buffer is visible,
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you can call @code{set-buffer-window} to display it in a window again.
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@defun set-window-fringes window left &optional right outside-margins
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This function sets the fringe widthes of window @var{window}.
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If window is @code{nil}, that stands for the selected window.
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The argument @var{left} specifies the width in pixels of the left
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fringe, and likewise @var{right} for the right fringe. A value of
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@code{nil} for either one stands for the default width. If
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@var{outside-margins} is non-@code{nil}, that specifies that fringes
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should appear outside of the display margins.
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@end defun
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@defun window-fringes window
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This function returns information about the fringes of a window
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@var{window}. The value as the form @code{(@var{left-width}
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@var{right-width} @var{frames-outside-margins}).
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@end defun
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@node Display Property
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@section The @code{display} Property
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@cindex display specification
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@ -3225,9 +3461,9 @@ buffers that do not override it. @xref{Default Value}.
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@defopt indicate-empty-lines
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@tindex indicate-empty-lines
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@cindex fringes, and empty line indication
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When this is non-@code{nil}, Emacs displays a special glyph in
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each empty line at the end of the buffer, on terminals that
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support it (window systems).
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When this is non-@code{nil}, Emacs displays a special glyph in the
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fringe of each empty line at the end of the buffer, on terminals that
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support it (window systems). @xref{Fringes}.
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@end defopt
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@defopt tab-width
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