Internally Polymode uses indirect buffers to implement inner spans of different modes. Each inner major mode within a polymode buffer has its own indirect buffer associated with it. Host mode lives in the base buffer. Therefore, switching modes in Polymode is as fast as switching emacs buffers because it never re-installs major modes like most of other MMM frameworks do. Dave Love's multi-mode.el gets full credit for this idea.

By sibling buffers we mean base or indirect buffers which are shared with the current buffer.


  • span is a contiguous and homogeneous region of text of the same Emacs major mode. There are 4 types of spans: head, body, tail and host.
    All spans are closed on the left and open on the right. For example, a span spanning [3, 5) contains character at position 3 but not at position 5. This is consistent with how emacs' functions deal with text properties.

  • chunk is a contiguous region that consists of one or more spans. There are two major types of chunks:

    • host chunks which contain only one span in the host major mode.
    • inner chunks which commonly consists of head, body and tail, where body is of some other mode than host.
  • polymode means one of the following:

    1. a sum of related functionality available in emacs buffers
    2. function which installs a bunch of functionality into emacs buffers.
      Polymodes can be used like any other emacs major mode (for example placed in auto-mode-alist), or like a minor mode in order to install functionality on top of an existing emacs mode.
    3. an object of class pm-polymode which holds the configuration for the polymode.
  • chunkmode, and the more specific hostmode and innermode mean either:

    1. a sum of related functionality in host and inner chunks
    2. configuration objects derived from pm-chunkmode class (pm-host-hostmode, pm-inner-innermode, pm-inner-auto-chunkmode).


Host and inner chunks are configured through objects derived from pm-chunkmode class and are generically referred to as "chunkmodes". These objects have named of the form poly-XYZ-hostmode and poly-XYZ-innermode and are refereed to as hostmodes and innermodes respectively.

Polymodes are configured through objects of class pm-polymode which are named with poly-XYZ-polymode scheme where XYZ is the same as in the polymode function poly-XYZ-mode. During initialization of the polymodes the poly-XYZ-polymode object is cloned and stored in a buffer-local variable pm/polymode. This object is shared across all sibling buffers.

Chunks and chunkmodes are different concepts. Chunk is a fragments of text and there might be multiple chunks of the same mode within a buffer. In contrast, there is only one chunkmode of some type per buffer and the "behavior" in each chunk is determined by the chunkmode.

Class Hierarchy

Polymode package uses eieio to represent its objects. The root class for all polymode classes is eieio-instance-inheritor which provides prototype based inheritance. This means that objects instantiated from polymode classes can be cloned in order to dynamically create a hierarchy of customizable objects.

Instance inheritance (or prototype inheritance) means that if you change a slot of a parent object, all of the children and grand-children of the object will inherit the new value unless they explicitly overwrite that slot.

There are a bunch of such objects already defined, you can check those in polymodes, poly-hostmodes and poly-innermodes customization groups.

Polymode class hierarchy:

            |    +--pm-inner-chunkmode
            |    |    +--pm-inner-auto-chunkmode
            |    +--pm-host-chunkmode
            |    +--pm-shell-weaver
            |    +--pm-callback-weaver

Using Help with EIEIO: Each eieio class has a corresponding constructor whose docstring contains a complete description of the class.

General Naming Conventions

User facing functionality is named with polymode- prefix. Polymodes are named with poly-XYZ-mode convention. Host, inner and polymode configuration objects are named poly-XYZ-hostmode, poly-XYZ-innermode and poly-name-polymode. Classes, methods and developer-oriented API have pm- prefix.