Cool features in Emacs 26

    ** Emacs now provides a limited form of concurrency with Lisp threads.
    Concurrency in Emacs Lisp is "mostly cooperative", meaning that
    Emacs will only switch execution between threads at well-defined
    times: when Emacs waits for input, during blocking operations related
    to threads (such as mutex locking), or when the current thread
    explicitly yields.  Global variables are shared among all threads, but
    a 'let' binding is thread-local.  Each thread also has its own current
    buffer and its own match data.

    See the chapter "Threads" in the ELisp manual for full documentation
    of these facilities.
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    ** 'C-x h' ('mark-whole-buffer') will now avoid marking the prompt
    part of minibuffers.
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    ** 'align-regexp' has a separate history for its interactive argument.
    'align-regexp' no longer shares its history with all other
    history-less functions that use 'read-string'.
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    ** The networking code has been reworked so that it's more
    asynchronous than it was (when specifying :nowait t in
    'make-network-process').  How asynchronous it is varies based on the
    capabilities of the system, but on a typical GNU/Linux system the DNS
    resolution, the connection, and (for TLS streams) the TLS negotiation
    are all done without blocking the main Emacs thread.  To get
    asynchronous TLS, the TLS boot parameters have to be passed in (see
    the manual for details).

    Certain process oriented functions (like 'process-datagram-address')
    will block until socket setup has been performed.  The recommended way
    to deal with asynchronous sockets is to avoid interacting with them
    until they have changed status to "run".  This is most easily done
    from a process sentinel.
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    ** Emacsclient has a new option -T/--tramp.
    This helps with using a local Emacs session as the server for a remote
    emacsclient.  With appropriate setup, one can now set the EDITOR
    environment variable on a remote machine to emacsclient, and
    use the local Emacs to edit remote files via Tramp.  See the node
    "emacsclient Options" in the user manual for the details.
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    ** Two new commands for finding the source code of Emacs Lisp
    libraries: 'find-library-other-window' and 'find-library-other-frame'.
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    ** The new variable 'display-raw-bytes-as-hex' allows to change the
    display of raw bytes from octal to hex.
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    ** Emacs now supports optional display of line numbers in the buffer.
    This is similar to what linum-mode provides, but much faster and
    doesn't usurp the display margin for the line numbers.  Customize the
    buffer-local variable 'display-line-numbers' to activate this optional
    display.  Alternatively, you can use the `display-line-numbers-mode'
    minor mode or the global `global-display-line-numbers-mode'.  When
    using these modes, customize `display-line-numbers-type' with the same
    value as you would use with `display-line-numbers'.

    Line numbers are not displayed at all in minibuffer windows and in
    tooltips, as they are not useful there.

    Lisp programs can disable line-number display for a particular screen
    line by putting the 'display-line-numbers-disable' text property or
    overlay property on the first character of that screen line.  This is
    intended for add-on packages that need a finer control of the display.

    Lisp programs that need to know how much screen estate is used up for
    line-number display in a window can use the new function
    'line-number-display-width'.

    Linum mode and all similar packages are henceforth becoming obsolete.
    Users and developers are encouraged to switch to this new feature
    instead.
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    ** The 'occur' command can now operate on the region.
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    ** New bindings for 'query-replace-map'.
    'undo', undo the last replacement; bound to 'u'.
    'undo-all', undo all replacements; bound to 'U'.
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    ** Emacs no longer prompts about editing a changed file when the file's
    content is unchanged.  Instead of only checking the modification time,
    Emacs now also checks the file's actual content before prompting the user.
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    ** New command 'replace-buffer-contents'.
    This command replaces the contents of the accessible portion of the
    current buffer with the contents of the accessible portion of a
    different buffer while keeping point, mark, markers, and text
    properties as intact as possible.
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    *** You can answer 'all' in 'dired-do-delete' to delete recursively all
    remaining directories without more prompts.
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    *** You can now use '`?`' in 'dired-do-shell-command'.
    It gets replaced by the current file name, like ' ? '.
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    *** In wdired, when editing files to contain slash characters,
    the resulting directories are automatically created.  Whether to do
    this is controlled by the 'wdired-create-parent-directories' variable.
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    *** 'W' is now bound to 'browse-url-of-dired-file', and is useful for
    viewing HTML files and the like.
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    *** New 'M-RET' command for opening a link at point in a new eww buffer.
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    *** A new 's' command for switching to another eww buffer via the minibuffer.
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    *** New connection method "gdrive", which allows to access Google
    Drive onsite repositories.
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    *** Tramp is able now to send SIGINT to remote asynchronous processes.
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    *** Support for completing attribute values, at-rules, bang-rules,
    HTML tags, classes and IDs using the 'completion-at-point' command.
    Completion candidates for HTML classes and IDs are retrieved from open
    HTML mode buffers.
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    *** CSS mode now binds 'C-h S' to a function that will show
    information about a CSS construct (an at-rule, property, pseudo-class,
    pseudo-element, with the default being guessed from context).  By
    default the information is looked up on the Mozilla Developer Network,
    but this can be customized using 'css-lookup-url-format'.
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    *** CSS colors are fontified using the color they represent as the
    background.  For instance, #ff0000 would be fontified with a red
    background.
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    *** Opening a .h file will turn C or C++ mode depending on language used.
    This is done with the help of 'c-or-c++-mode' function which analyses
    contents of the buffer to determine whether it's a C or C++ source
    file.
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    *** Enchant is now supported as a spell-checker.

    Enchant is a meta-spell-checker that uses providers
    such as Hunspell to do the actual checking.  With it, users can use
    spell-checkers not directly supported by Emacs, such as Voikko, Hspell
    and AppleSpell, more easily share personal word-lists with other
    programs, and configure different spelling-checkers for different
    languages.  (Version 2.1.0 or later of Enchant is required.)
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    *** A new submode of 'html-mode', 'mhtml-mode', is now the default
    mode for *.html files.  This mode handles indentation,
    fontification, and commenting for embedded JavaScript and CSS.
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    ** New major mode 'less-css-mode' (a minor variant of 'css-mode') for
    editing Less files.
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    ** 'C-up', 'C-down', 'C-left' and 'C-right' are now defined in term
    mode to send the same escape sequences that xterm does.  This makes
    things like forward-word in readline work.
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    ** 'min' and 'max' no longer round their results.
    Formerly, they returned a floating-point value if any argument was
    floating-point, which was sometimes numerically incorrect.  For
    example, on a 64-bit host (max 1e16 10000000000000001) now returns its
    second argument instead of its first.
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    ** To avoid confusion caused by "smart quotes", the reader no longer
    accepts Lisp symbols which begin with the following quotation
    characters: ‘’‛“”‟〞＂＇, unless they are escaped with backslash.
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    ** The function 'assoc' now takes an optional third argument TESTFN.
    This argument, when non-nil, is used for comparison instead of
    'equal'.
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    ** The new function 'buffer-hash' computes a fast, non-consing hash of
    a buffer's contents.
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    ** 'car' and 'cdr' compositions 'cXXXr' and 'cXXXXr' are now part of Elisp.
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    ** 'gensym' is now part of Elisp.
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    ** Intercepting hotkeys on Windows 7 and later now works better.
    The new keyboard hooking code properly grabs system hotkeys such as
    Win-* and Alt-TAB, in a way that Emacs can get at them before the
    system.  This makes the 'w32-register-hot-key' functionality work
    again on all versions of MS-Windows starting with Windows 7.  On
    Windows NT and later you can now register any hotkey combination.  (On
    Windows 9X, the previous limitations, spelled out in the Emacs manual,
    still apply.)
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    ** 'process-attributes' on Darwin systems now returns more information.
THIS MEANS M-x proced WORKS NOW ON OSX!!!
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    ** Mousewheel and trackpad scrolling on macOS 10.7+ now behaves more
    like the macOS default.  The new variables 'ns-mwheel-line-height',
    'ns-use-mwheel-acceleration' and 'ns-use-mwheel-momentum' can be used
    to customize the behavior.