objects as sequence objects.  In this context, they
act as if they were lists (yes, they are mutable) of strings, with each
element being a line of the buffer.  All of the usual sequence operations,
including indexing, index assignment, slicing and slice assignment, work as
you would expect.  Note that the result of indexing (slicing) a buffer is a
string (list of strings).  This has one unusual consequence - b[:] is different
from b.  In particular, "b[:] = None" deletes the whole of the buffer, whereas
"b = None" merely updates the variable b, with no effect on the buffer.

Buffer indexes start at zero, as is normal in Python.  This differs from vim
line numbers, which start from 1.  This is particularly relevant when dealing
with marks (see below) which use vim line numbers.

The buffer object attributes are:
	b.vars		Dictionary-like object used to access
			|buffer-variable|s.
	b.options	Mapping object (supports item getting, setting and
			deleting) that provides access to buffer-local options
			and buffer-local values of |global-local| options. Use
			|python-window|.options if option is window-local,
			this object will raise KeyError. If option is
			|global-local| and local value is missing getting it
			will return None.
	b.name		String, RW. Contains buffer name (full path).
			Note: when assigning to b.name |BufFilePre| and
			|BufFilePost| autocommands are launched.
	b.number	Buffer number. Can be used as |python-buffers| key.
			Read-only.
	b.valid		True or False. Buffer object becomes invalid when
			corresponding buffer is wiped out.

The buffer object methods are:
	b.append(str)	Append a line to the buffer
	b.append(str, nr)  Idem, below line "nr"
	b.append(list)	Append a list of lines to the buffer
			Note that the option of supplying a list of strings to
			the append method differs from the equivalent method
			for Python's built-in list objects.
	b.append(list, nr)  Idem, below line "nr"
	b.mark(name)	Return a tuple (row,col) representing the position
			of the named mark (can also get the []"<> marks)
	b.range(s,e)	Return a range object (see |python-range|) which
			represents the part of the given buffer between line
			numbers s and e |inclusive|.

Note that when adding a line it must not contain a line break character '\n'.
A trailing '\n' is allowed and ignored, so that you can do: >vim
	:py b.append(f.readlines())

Buffer object type is available using "Buffer" attribute of vim module.

Examples (assume b is the current buffer) >vim
	:py print(b.name)		# write the buffer file name
	:py b[0] = "hello!!!"		# replace the top line
	:py b[:] = None			# delete the whole buffer
	:py del b[:]			# delete the whole buffer
	:py b[0:0] = [ "a line" ]	# add a line at the top
	:py del b[2]			# delete a line (the third)
	:py b.append("bottom")		# add a line at the bottom
	:py n = len(b)			# number of lines
	:py (row,col) = b.mark('a')	# named mark
	:py r = b.range(1,5)		# a sub-range of the buffer
	:py b.vars["foo"] = "bar"	# assign b:foo variable
	:py b.options["ff"] = "dos"	# set fileformat
	:py del b.options["ar"]		# same as :set autoread<

==============================================================================
Range objects						*python-range*

Range objects represent a part of a vim buffer.  You can obtain them in a
number of ways:
	- via vim.current.range (|python-current|)
	- from a buffer's range() method (|python-buffer|)

A range object is almost identical in operation to a buffer object.  However,
all operations are restricted to the lines within the range (this line range
can, of course, change as a result of slice assignments, line deletions, or
the range.append() method).

The range object attributes are:
	r.start		Index of first line into the buffer
	r.end		Index of last line into the buffer

The range object methods are:
	r.append(str)	Append a line to the range
	r.append(str, nr)  Idem, after line "nr"
	r.append(list)	Append a list of lines to the range
			Note that the option of supplying a