Use "@code{nil}" in documentation

doc/lispref/display.texi

@@ -2142,7 +2142,7 @@ the buffer might contain long lines that will be truncated anyway.
 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
 maximum Y coordinate beyond which text is to be ignored; it is
 therefore also the maximum pixel-height that the function can return.
-If @var{y-limit} is nil or omitted, it means to considers all the
+If @var{y-limit} is @code{nil} or omitted, it means to consider all the
 lines of text till the buffer position specified by @var{to}.  Since
 calculating the pixel-height of a large buffer can take some time, it
 makes sense to specify this argument; in particular, if the caller
@@ -7517,7 +7517,7 @@ end of the buffer continues from the other end.  If
 @var{display-message} is non-@code{nil}, the button's help-echo string
 is displayed.  Any button with a non-@code{nil} @code{skip} property
 is skipped over.  Returns the button found, and signals an error if no
-buttons can be found.  If @var{no-error} is non-@code{nil}, return nil
+buttons can be found.  If @var{no-error} is non-@code{nil}, return @code{nil}
 instead of signaling the error.
 @end deffn
 
@@ -7529,7 +7529,7 @@ end of the buffer continues from the other end.  If
 @var{display-message} is non-@code{nil}, the button's help-echo string
 is displayed.  Any button with a non-@code{nil} @code{skip} property
 is skipped over.  Returns the button found, and signals an error if no
-buttons can be found.  If @var{no-error} is non-@code{nil}, return nil
+buttons can be found.  If @var{no-error} is non-@code{nil}, return @code{nil}
 instead of signaling the error.
 @end deffn
 

doc/lispref/functions.texi

@@ -1616,7 +1616,7 @@ were a local variable that had been captured by static scoping.
 
 @defun oclosure-type object
 This function returns the OClosure type (a symbol) of @var{object} if it is an
-OClosure, and nil otherwise.
+OClosure, and @code{nil} otherwise.
 @end defun
 
 

doc/lispref/keymaps.texi

@@ -1643,7 +1643,7 @@ non-@code{nil}, the definition will be removed.  This is almost the
 same as setting the definition to @code{nil}, but makes a difference
 if the @var{keymap} has a parent, and @var{key} is shadowing the same
 binding in the parent.  With @var{remove}, subsequent lookups will
-return the binding in the parent, and with a nil @var{def}, the
+return the binding in the parent, whereas with a @code{nil} definition the
 lookups will return @code{nil}.
 @end defun
 

doc/lispref/os.texi

@@ -1528,7 +1528,7 @@ integer, it specifies a clock frequency and this function returns an
 integer-pair timestamp @code{(@var{ticks} . @var{form})}.  If @var{form} is
 @code{t}, this function treats it as a positive integer suitable for
 representing the timestamp; for example, it is treated as 1000000000
-if @var{time} is nil and the platform timestamp has nanosecond
+if @var{time} is @code{nil} and the platform timestamp has nanosecond
 resolution.  If @var{form} is @code{list}, this function returns an
 integer list @code{(@var{high} @var{low} @var{micro} @var{pico})}.
 Although an omitted or @code{nil} @var{form} currently acts like

doc/lispref/symbols.texi

@@ -775,7 +775,7 @@ For most purposes, when the flag variable
 @code{symbols-with-pos-enabled} is non-@code{nil}, symbols with
 positions behave just as bare symbols do.  For example, @samp{(eq
 #<symbol foo at 12345> foo)} has a value @code{t} when that variable
-is set (but nil when it isn't set).  Most of the time in Emacs this
+is set (but @code{nil} when it isn't set).  Most of the time in Emacs this
 variable is @code{nil}, but the byte compiler binds it to @code{t}
 when it runs.