Docstring improvements

* src/xdisp.c (syms_of_xdisp):
* src/keyboard.c (syms_of_keyboard):
* src/buffer.c (syms_of_buffer):
Docstring improvements.

src/buffer.c

@@ -5897,6 +5897,8 @@ variable specifies the size of the narrowed region around point.
 
 To disable that narrowing, set this variable to 0.
 
+See also `long-line-locked-narrowing-bol-search-limit'.
+
 There is no reason to change that value except for debugging purposes.  */);
   long_line_locked_narrowing_region_size = 500000;
 
@@ -5912,7 +5914,7 @@ narrowed buffer, with a narrowing locked with `narrowing-lock'.  The
 variable `long-line-locked-narrowing-region-size' specifies the size
 of the narrowed region around point.  This variable, which should be a
 small integer, specifies the number of characters by which that region
-can be extended backwards to start it at the beginning of a line.
+can be extended backwards to make it start at the beginning of a line.
 
 There is no reason to change that value except for debugging purposes.  */);
   long_line_locked_narrowing_bol_search_limit = 128;

src/keyboard.c

@@ -12727,7 +12727,8 @@ the error might happen repeatedly and make Emacs nonfunctional.
 
 Note that, when the current buffer contains one or more lines whose
 length is above `long-line-threshold', these hook functions are called
-with the buffer narrowed to a small portion around point, and the
+with the buffer narrowed to a small portion around point (whose size
+is specified by `long-line-locked-narrowing-region-size'), and the
 narrowing is locked (see `narrow-to-region'), so that these hook
 functions cannot use `widen' to gain access to other portions of
 buffer text.
@@ -12748,7 +12749,8 @@ avoid making Emacs unresponsive while the user types.
 
 Note that, when the current buffer contains one or more lines whose
 length is above `long-line-threshold', these hook functions are called
-with the buffer narrowed to a small portion around point, and the
+with the buffer narrowed to a small portion around point (whose size
+is specified by `long-line-locked-narrowing-region-size'), and the
 narrowing is locked (see `narrow-to-region'), so that these hook
 functions cannot use `widen' to gain access to other portions of
 buffer text.

src/xdisp.c

@@ -36745,10 +36745,11 @@ fontify a region starting at POS in the current buffer, and give
 fontified regions the property `fontified' with a non-nil value.
 
 Note that, when the buffer contains one or more lines whose length is
-above `long-line-threshold', these functions are called with the buffer
-narrowed to a small portion around POS, and the narrowing is locked (see
-`narrow-to-region'), so that these functions cannot use `widen' to gain
-access to other portions of buffer text.  */);
+above `long-line-threshold', these functions are called with the
+buffer narrowed to a small portion around POS (whose size is specified
+by `long-line-locked-narrowing-region-size'), and the narrowing is
+locked (see `narrow-to-region'), so that these functions cannot use
+`widen' to gain access to other portions of buffer text.  */);
   Vfontification_functions = Qnil;
   Fmake_variable_buffer_local (Qfontification_functions);