Calling |nvim_buf_attach()| with send_buffer=true on an empty buffer, emits: >
    nvim_buf_lines_event[{buf}, {changedtick}, 0, -1, [""], v:false]

User adds two lines to the buffer, emits: >
    nvim_buf_lines_event[{buf}, {changedtick}, 0, 0, ["line1", "line2"], v:false]

User moves to a line containing the text "Hello world" and inserts "!", emits: >
    nvim_buf_lines_event[{buf}, {changedtick}, {linenr}, {linenr} + 1,
                         ["Hello world!"], v:false]

User moves to line 3 and deletes 20 lines using "20dd", emits: >
    nvim_buf_lines_event[{buf}, {changedtick}, 2, 22, [], v:false]

User selects lines 3-5 using |linewise-visual| mode and then types "p" to
paste a block of 6 lines, emits: >
    nvim_buf_lines_event[{buf}, {changedtick}, 2, 5,
      ['pasted line 1', 'pasted line 2', 'pasted line 3', 'pasted line 4',
       'pasted line 5', 'pasted line 6'],
      v:false
    ]

User reloads the buffer with ":edit", emits: >
    nvim_buf_detach_event[{buf}]
<

LUA ~
                                                        *api-buffer-updates-lua*
In-process Lua plugins can receive buffer updates in the form of Lua
callbacks. These callbacks are called frequently in various contexts;
|textlock| prevents changing buffer contents and window layout (use
|vim.schedule()| to defer such operations to the main loop instead).
Moving the cursor is allowed, but it is restored afterwards.

|nvim_buf_attach()| will take keyword args for the callbacks. "on_lines" will
receive parameters ("lines", {buf}, {changedtick}, {firstline}, {lastline},
{new_lastline}, {old_byte_size} [, {old_utf32_size}, {old_utf16_size}]).
Unlike remote channel events the text contents are not passed. The new text can
be accessed inside the callback as >lua

    vim.api.nvim_buf_get_lines(buf, firstline, new_lastline, true)
<
{old_byte_size} is the total size of the replaced region {firstline} to
{lastline} in bytes, including the final newline after {lastline}. if
`utf_sizes` is set to true in |nvim_buf_attach()| keyword args, then the
UTF-32 and UTF-16 sizes of the deleted region is also passed as additional
arguments {old_utf32_size} and {old_utf16_size}.

"on_changedtick" is invoked when |b:changedtick| was incremented but no text
was changed. The parameters received are ("changedtick", {buf}, {changedtick}).

                                                        *api-lua-detach*
In-process Lua callbacks can detach by returning `true`. This will detach all
callbacks attached with the same |nvim_buf_attach()| call.


==============================================================================
Buffer highlighting                                            *api-highlights*

Nvim allows plugins to add position-based highlights to buffers. This is
similar to |matchaddpos()| but with some key differences. The added highlights
are associated with a buffer and adapts to line insertions and deletions,
similar to signs. It is also possible to manage a set of highlights as a group
and delete or replace all at once.

The intended use case are linter or semantic highlighter plugins that monitor
a buffer for changes, and in the background compute highlights to the buffer.
Another use case are plugins that show output in an append-only buffer, and
want to add highlights to the outputs. Highlight data cannot be preserved
on writing and loading a buffer to file, nor in undo/redo cycles.

Highlights are registered using the |nvim_buf_set_extmark()| function, which
adds highlights as |extmarks|. If highlights need to be tracked or manipulated
after adding them, the returned |extmark| id can be used. >lua
  -- create the highlight through an extmark
  extid = vim.api.nvim_buf_set_extmark(buf, ns_id, line, col_start, {end_col = col_end, hl_group = hl_group})

  -- example: modify the extmark's highlight group
  vim.api.nvim_buf_set_extmark(buf, ns_id, line, col_start, {end_col = col_end, hl_group = NEW_HL_GROUP, id = extid})

  -- example: change the highlight's