= Scopes

== Description

Scopes are groups in which a particular Kakoune object can have different
values depending on the group the value was declared in.

These scoped objects are:

- aliases (See <<commands#,`:doc commands`>>)
- faces (See <<faces#,`:doc faces`>>)
- highlighters (See <<highlighters#,`:doc highlighters`>>)
- hooks (See <<hooks#,`:doc hooks`>>)
- keymaps (See <<mapping#,`:doc mapping`>>)
- options (See <<options#,`:doc options`>>)

== Names and hierarchy

Scopes are named as follows:

*window*::
    context linked to the window displaying a buffer.

    In Kakoune, the concept of a *window* must not be confused with
    the concept of a window at the OS level.
    In other terms, a window is *not* a client (like a terminal or GUI)
    but one of many 'views' into a buffer.

    There is a N:1 relationship between windows and buffers; once a 
    window is linked to a buffer, the window's buffer never changes.
    Windows store a set of selections and the scroll position.

*buffer*::
    context linked directly to the buffer

*global*::
    global context linked to the instance of Kakoune

*local*::
    A local scope is inserted by each *evaluate-commands* invocations
    for its duration. Nested *evaluate-commands* each inject a new
    local scope whose parent is the previous local scope. User declared
    commands defined with *define-command* also introduce a local scope
    while executing.

    A local scope is intended for temporarily overwriting some scoped
    value, such as an option or an alias.


The following order of priority applies to the above scopes:

-----------------------------------
local ]> window ]> buffer ]> global
-----------------------------------

The above priority line implies that objects can have individual values
that will be resolved first in the *local* scope (if it exists), then the
*window* scope, then in the *buffer* scope, and finally in the *global*
scope.

Normally, the *buffer* scope keyword means the scope associated with the
currently active buffer, but it's possible to specify any existing buffer by
adding an `=` and the value of `%val{buffile}` for that buffer
(See <<expansions#value-expansions,`:doc expansions value-expansions`>>).
For example, to set the `indentwidth` option for the `/etc/fstab` buffer::

----
set-option buffer=/etc/fstab indentwidth 8
----

The `set-option` and `unset-option` commands also accept *current* as 
a valid scope name. It refers to the narrowest scope the option is set in.

== Uses

The scope paradigm is very useful as it allows the user to customize the
behavior of the editor without modifying the configuration globally, as
is the case with other editors who only have a single *global* scope by
default.

Examples:

*filetype*::
    A single buffer opened in two separate windows can have different
    filetypes declared in the *window* scope with 'set-option'.
    (See <<options#,`:doc options`>>)

*status line*::
    All the buffers of the current session can have the same information
    displayed in the status line, except for a specific buffer (the
    'modelinefmt' option can be declared in the *global* scope, and
    customized in the *buffer* scope with 'set-option'.
    (See <<options#,`:doc options`>>)

== Execution context

Some commands work in a specific context that might exclude one or
several scopes altogether, consequently ignoring some values of a given
object.

Example: the *window* scope is never considered when resolving the
values of options when writing a buffer (e.g. 'BOM', 'eolformat').
