It doesn't, with rare exceptions.

[[Details.]]

[TCT] takes memory leaks [[ref]] very seriously.  Few ever escape into a release, 
and few known ones survive long.

'''However''', there are at least an order of magnitude more ''perceived'' memory 
leaks.  These result mainly from two causes:
   * mis-measured memory use
   * userland, or application-level, memory leaks.

[[More explanation.]]

[[Pertinent post
[http://groups-beta.google.com/group/comp.lang.tcl/msg/35e50b74fbc0d729]
by [tclguy] on [Tcl]'s allocator, high-water marking, ...]]


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Also of interest:  
   * "[memory]"
   * "[memory leak finding with memory trace]"
   * "[Why Do Programs Take Up So Much Memory ?]"
   * "[How to debug memory faults in Tcl and extensions]"
   * "[Memory introspection]"
   * "[Measuring memory usage]"
   * "[Memory Footprint Comparisons]"
   * "[Memory costs with Tcl]"