**Object Oriented Programming**
The commands of the '''[TclOO]''' package are now
part of Tcl itself.  This gives Tcl a built-in object
system that is fully dynamic, class-based, and includes
advanced features such as meta-classes, filters, and mixins.

New version 4 of the popular package Itcl (aka '''incr Tcl''') is also
included, granting support for some traditional OO Tcl programming
out of the box as well.

**Stackless Evaluation**
The evaluation of many levels of nested '''[proc]''' calls are no longer
implemented as a stack of nested C routine calls.  This revision in
the internal implementation of Tcl evaluation makes deep recursion in
Tcl scripts safe to do.  But there's more...

This new implementation enables a collection of new commands,
'''[coroutine]''', '''[tailcall]''', '''[yield]''', and '''[yieldto]''' that
provide profound new capabilities and models of concurrency to
Tcl scripts.

**Enhanced Exceptions**
New commands '''[try]''' and '''[throw]''' and a wealth of new
'''-errorcode''' values enable far more precise
trapping and handling of exceptions using a familiar construct.

**Batteries Included**
Tcl delivers in the '''pkgs''' subdirectory a bundled collection
of third-party packages built and installed along with Tcl.

**Thread-enabled Operations**
A thread-enabled default build, a bundled
'''[Thread]''' package, and new command '''[interp cancel]''' make
Tcl 8.6 ready for your multi-threaded programming tasks.

**SQL Database Powered**
The bundled Tcl DataBase Connectivity ('''[tdbc]''') interface package
makes it possible to write your SQL database-powered scripts decoupled
from any particular database engine.  The bundled '''[SQLite%|%sqlite3]''' and
'''tdbc::sqlite3''' packages supply a powerful and popular SQL
database engine ready to use.

**IPv6 Networking**
The '''[socket]''' command now recognizes numeric IPv6 addresses
as valid values for its ''$host'' argument where platform
support exists.

**Built-in Zlib Compression**
New command '''[zlib]''' provides utilities to handle compression
of data and streams.

**List Processing**
New commands '''[lmap]''' and '''[dict map]''' enable the elegant
expression of transformations over Tcl containers.

**Stacked Channels by Script**
New commands '''[chan push]''' and '''[chan pop]''' expose the power
of stacked channels without the need to write C code.

**Other New Features**
Temporary '''[file]''' creation, enhancements to list sorting and setting,
'''[dict]''' filtering, half-close of bidirectional channels, encoding
and decoding of '''[binary]''' sequences, finer control over '''[load]''',
and many many more.  Every new feature is important to somebody.
See [Changes in Tcl/Tk 8.6] or [http://tip.tcl.tk/311%|%TIP #311] for
the complete list.

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