An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.
In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, independent values of point, independent narrowing, independent markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), independent major modes, and independent buffer-local variable bindings.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.
This creates and returns an indirect buffer named name whose base buffer is base-buffer. The argument base-buffer may be a live buffer or the name (a string) of an existing buffer. If name is the name of an existing buffer, an error is signaled.
If clone is non-nil, then the indirect buffer originally shares the state of base-buffer such as major mode, minor modes, buffer local variables and so on. If clone is omitted or nil the indirect buffer’s state is set to the default state for new buffers.
If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer. If, in addition, clone is non-nil, the initial state is copied from the actual base buffer, not from base-buffer.
This function creates and returns a new indirect buffer that shares the current buffer’s base buffer and copies the rest of the current buffer’s attributes. (If the current buffer is not indirect, it is used as the base buffer.)
If display-flag is non-nil, as it always is in interactive calls, that means to display the new buffer by calling pop-to-buffer. If norecord is non-nil, that means not to put the new buffer to the front of the buffer list.
This function returns the base buffer of buffer, which defaults to the current buffer. If buffer is not indirect, the value is nil. Otherwise, the value is another buffer, which is never an indirect buffer.
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Licensed under the GNU GPL license.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Indirect-Buffers.html