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I noticed that [Unicode has slots for the decomposition type of
kanji](http://www.alanwood.net/unicode/ideographic_description_characters.html).
I have been wondering why it has only 12 slots (and doesn't even include a
slot for "indecomposable", an empty box for a character like 木).

I can come up with more decomposition types, e.g. a long box on top and two
small boxes on the bottom, for a character like 森.

Is it general practice to only distinguish the 12 types listed in Unicode? Is
森 analysed as being of something like "primary decomposition type" top (木) and
bottom (林)?
CC BY-SA 3.0
2014-03-02T18:45:10.217
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question
kanji
Decomposition of kanji
While characters can be broken down into individual elements in a wide variety
of ways, the Ideographic Description Characters in Unicode represent the most
common, and in fact provide a substantial amount of coverage if one views
deconstruction as a matter of recursion.

For example, 森 is 木+林 in a stacked configuration: ⿱. 林 is 木+木 side-by-side: ⿰.
Nested within each other you effectively get your long box over two short
boxes, but semantically that's not how the character works.
CC BY-SA 3.0
2014-03-17T18:03:05.423
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answer
The intended purpose of the Ideographic Description Characters is for
describing characters that are _not_ encoded in Unicode (see [page 423 of the
standard](http://www.unicode.org/versions/Unicode6.2.0/ch12.pdf)) in an
Ideographic Description Sequence (IDS)---combinations of these characters and
existing CJK characters.

At the time they were first introduced (Unicode 3.0) there were "only" ~27,000
CJK characters encoded (now there's over 75,000), and an IDS could be used to
talk about CJK characters that did not exist in Unicode as compositions of
those that did (which is why there is no marker for "indecomposable" and they
are printable characters). That is, they are not intended to contain any
particular semantic of etymological content (although they certainly can be
used in that way). They are also not intended to be comprehensive---there are
characters that cannot be decomposed because the required components do not
exist (for example: 㣲, 莵, ...).

As far as Unicode is concerned, there is no canonical way of decomposing a
character. The group behind them (the Ideographic Rapporteur Group) [have made
some
suggestions](https://drive.google.com/uc?id=1CkJLIcX8ktcJbbUChqZ31qLFGkfXPcoB&export=download)
about how to do so, and [CHISE project has come up
with](http://www.kanji.zinbun.kyoto-u.ac.jp/projects/chise/ids/index.html) a
decomposition almost all of the existing CJK blocks in Unicode---but these are
not rules or an established standard. So 森 could be ⿱木林 or ⿱木⿰木木 (but I think
shorter sequences are preferred).

There are also some "missing" combinations. For example, there are surrounds
for the top-right (⿺), bottom-left (⿹), and bottom-right (⿸), but not top-
left. And similarly for surrounds above (⿵), below (⿶), and left (⿷), but not
right.
CC BY-SA 4.0
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answer