Reserved character codes in Unicode - unicode

Question

Why Unicode has several reserved character codes?
See the Unicode for two languages- Kannada and Tamil.
Both language are very old and I think there is no chance to get new characters to these languages.
EDIT: Then why are they wasting some character codes by making it reserved character codes?
Why are they not placing the reserved character codes at the end of each language character set?

Answer 1

This has to do with how the Unicode consortium doles out its allocated blocks, scripts, and code points. For example, in Block=Tamil, the start of it runs this way:
$ unichars '\p{Block=Tamil}' | head -20
U+00B82 ‭ ◌ஂ GC=Mn SC=Tamil TAMIL SIGN ANUSVARA
U+00B83 ‭ ஃ GC=Lo SC=Tamil TAMIL SIGN VISARGA
U+00B85 ‭ அ GC=Lo SC=Tamil TAMIL LETTER A
U+00B86 ‭ ஆ GC=Lo SC=Tamil TAMIL LETTER AA
U+00B87 ‭ இ GC=Lo SC=Tamil TAMIL LETTER I
U+00B88 ‭ ஈ GC=Lo SC=Tamil TAMIL LETTER II
U+00B89 ‭ உ GC=Lo SC=Tamil TAMIL LETTER U
U+00B8A ‭ ஊ GC=Lo SC=Tamil TAMIL LETTER UU
U+00B8E ‭ எ GC=Lo SC=Tamil TAMIL LETTER E
U+00B8F ‭ ஏ GC=Lo SC=Tamil TAMIL LETTER EE
U+00B90 ‭ ஐ GC=Lo SC=Tamil TAMIL LETTER AI
U+00B92 ‭ ஒ GC=Lo SC=Tamil TAMIL LETTER O
U+00B93 ‭ ஓ GC=Lo SC=Tamil TAMIL LETTER OO
U+00B94 ‭ ஔ GC=Lo SC=Tamil TAMIL LETTER AU
U+00B95 ‭ க GC=Lo SC=Tamil TAMIL LETTER KA
U+00B99 ‭ ங GC=Lo SC=Tamil TAMIL LETTER NGA
U+00B9A ‭ ச GC=Lo SC=Tamil TAMIL LETTER CA
U+00B9C ‭ ஜ GC=Lo SC=Tamil TAMIL LETTER JA
U+00B9E ‭ ஞ GC=Lo SC=Tamil TAMIL LETTER NYA
U+00B9F ‭ ட GC=Lo SC=Tamil TAMIL LETTER TTA
They tend to reserve contiguous rows of 4, 8, or 16 code points to all the same “kind” of character. Yes, there are gaps there, but it’s like how in the filesystem, once you allocate a sector (or block if you don’t have separate sectors within a block) to one file, even if that file doesn’t use everything in its (final) sector, you don’t go giving away those unused byte to some other process. Things tend to get padded to block boundaries anyway.
It’s not like we’re at any risk of running out of codes.
Here is the beginning of the allocated area starts with “Signs”, as shown by the first assigned code points in that block. The gap may represent a change from one kind of character to another. If you check out the first five code points in the block for their properties, you see that those unassigned code points still have the right block property:
$ uniprops -a U+00B80 U+00B81 U+00B82 U+00B83 U+00B84 U+00B85
U+0B80 ‹U+0B80› \N{U+0B80}
\pC \p{Cn}
All Any InTamil C Other Cn Unassigned Zzzz Unknown
Age=Unassigned Bidi_Class=L Bidi_Class=Left_To_Right BC=L Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered
CCC=NR Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=Unknown LB=XX Line_Break=XX Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=Unassigned IN=Unassigned Script=Unknown SC=Zzzz Script=Zzzz Sentence_Break=Other SB=XX
Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX
U+0B81 ‹U+0B81› \N{U+0B81}
\pC \p{Cn}
All Any InTamil C Other Cn Unassigned Zzzz Unknown
Age=Unassigned Bidi_Class=L Bidi_Class=Left_To_Right BC=L Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered
CCC=NR Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=Unknown LB=XX Line_Break=XX Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=Unassigned IN=Unassigned Script=Unknown SC=Zzzz Script=Zzzz Sentence_Break=Other SB=XX
Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX
U+0B82 ‹◌ஂ› \N{TAMIL SIGN ANUSVARA}
\w \pM \p{Mn}
All Any Alnum Alpha Alphabetic Assigned InTamil Tamil Is_Tamil Case_Ignorable CI M Mn Gr_Ext Grapheme_Extend Graph GrExt ID_Continue IDC
Mark Nonspacing_Mark Print Taml Word XID_Continue XIDC X_POSIX_Alnum X_POSIX_Alpha X_POSIX_Graph X_POSIX_Print X_POSIX_Word
Age=1.1 Bidi_Class=Nonspacing_Mark BC=NSM Bidi_Class=NSM Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered
CCC=NR Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=EX
Grapheme_Cluster_Break=Extend GCB=EX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=T Joining_Type=Transparent JT=T Line_Break=CM Line_Break=Combining_Mark LB=CM Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=1.1 IN=1.1 Present_In=2.0 IN=2.0 Present_In=2.1 IN=2.1 Present_In=3.0 IN=3.0 Present_In=3.1 IN=3.1
Present_In=3.2 IN=3.2 Present_In=4.0 IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1 Present_In=5.2 IN=5.2
Present_In=6.0 IN=6.0 Script=Tamil SC=Taml Script=Taml Sentence_Break=EX Sentence_Break=Extend SB=EX Word_Break=Extend WB=Extend
U+0B83 ‹ஃ› \N{TAMIL SIGN VISARGA}
\w \pL \p{L_} \p{Lo}
All Any Alnum Alpha Alphabetic Assigned InTamil Tamil Is_Tamil L Lo Gr_Base Grapheme_Base Graph GrBase ID_Continue IDC ID_Start IDS Letter
L_ Other_Letter Print Taml Word XID_Continue XIDC XID_Start XIDS X_POSIX_Alnum X_POSIX_Alpha X_POSIX_Graph X_POSIX_Print X_POSIX_Word
Age=1.1 Bidi_Class=L Bidi_Class=Left_To_Right BC=L Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered CCC=NR
Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=1.1 IN=1.1 Present_In=2.0 IN=2.0 Present_In=2.1 IN=2.1 Present_In=3.0 IN=3.0 Present_In=3.1 IN=3.1
Present_In=3.2 IN=3.2 Present_In=4.0 IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1 Present_In=5.2 IN=5.2
Present_In=6.0 IN=6.0 Script=Tamil SC=Taml Script=Taml Sentence_Break=LE Sentence_Break=OLetter SB=LE Word_Break=ALetter WB=LE
Word_Break=LE
U+0B84 ‹U+0B84› \N{U+0B84}
\pC \p{Cn}
All Any InTamil C Other Cn Unassigned Zzzz Unknown
Age=Unassigned Bidi_Class=L Bidi_Class=Left_To_Right BC=L Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered
CCC=NR Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=Unknown LB=XX Line_Break=XX Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=Unassigned IN=Unassigned Script=Unknown SC=Zzzz Script=Zzzz Sentence_Break=Other SB=XX
Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX
U+0B85 ‹அ› \N{TAMIL LETTER A}
\w \pL \p{L_} \p{Lo}
All Any Alnum Alpha Alphabetic Assigned InTamil Tamil Is_Tamil L Lo Gr_Base Grapheme_Base Graph GrBase ID_Continue IDC ID_Start IDS Letter
L_ Other_Letter Print Taml Word XID_Continue XIDC XID_Start XIDS X_POSIX_Alnum X_POSIX_Alpha X_POSIX_Graph X_POSIX_Print X_POSIX_Word
Age=1.1 Bidi_Class=L Bidi_Class=Left_To_Right BC=L Block=Tamil Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered CCC=NR
Canonical_Combining_Class=NR Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group
JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL Numeric_Type=None NT=None
Numeric_Value=NaN NV=NaN Present_In=1.1 IN=1.1 Present_In=2.0 IN=2.0 Present_In=2.1 IN=2.1 Present_In=3.0 IN=3.0 Present_In=3.1 IN=3.1
Present_In=3.2 IN=3.2 Present_In=4.0 IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1 Present_In=5.2 IN=5.2
Present_In=6.0 IN=6.0 Script=Tamil SC=Taml Script=Taml Sentence_Break=LE Sentence_Break=OLetter SB=LE Word_Break=ALetter WB=LE
Word_Break=LE
If you look at other allocated blocks, you see the same sort of thing. It doesn’t make sense to slice up blocks into unrelated things.
As I said, it’s not as though they’re going to run out of space, so I don’t know what the concern is here.
BTW, you can get Unicode exploration and proceesing tools like unichars, uniprops, uninames from my Unicode Command-Line Toolchest, either individually from there or the entire suite available through the CPAN Unicode::Tussle suite.