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53 lines
2.4 KiB
Markdown
53 lines
2.4 KiB
Markdown
[< back to index](../doc_index.md)
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### Defining custom encodings
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Every encoding is defined in an `.tbl` file with an appropriate name.
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The file is looked up in the directories on the include path, first directly, then in the `encoding` subdirectory.
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The file is a UTF-8 text file, with each line having a specific meaning.
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In the specifications below, `<>` are not to be meant literally:
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* lines starting with `#`, `;` or `//` are comments.
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* `ALIAS=<another encoding name>` defines this encoding to be an alias for another encoding.
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No other lines are allowed in the file.
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* `NAME=<name>` defines the name for this encoding. Required.
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* `BUILTIN=<internal name>` defines this encoding to be a UTF-based encoding.
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`<internal name>` may be one of `UTF-8`, `UTF-16LE`, `UTF-16BE`, `UTF-32LE`, `UTF-32BE`.
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If this directive is present, the only other allowed directive in the file is the `NAME` directive.
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* `EOT=<xx>` where `<xx>` are two hex digits, defines the string terminator byte.
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Required, unless `BUILTIN` is present.
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There have to be two digits, `EOT=0` is invalid.
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* lines like `<xx>=<c>` where `<xx>` are two hex digits
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and `<c>` is either a **non-whitespace** character or a **BMP** Unicode codepoint written as `U+xxxx`,
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define the byte `<xx>` to correspond to character `<c>`.
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There have to be two digits, `0=@` is invalid.
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* lines like `<xx>-<xx>=<c><c><c><c>` where `<c>` is repeated an appropriate number of times
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define characters for multiple byte values.
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In this kind of lines, characters cannot be represented as Unicode codepoints.
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* lines like `<c>=<xx>`, `<c>=<xx><xx>` etc.
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define secondary or alternate characters that are going to be represented as one or more bytes.
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There have to be two digits, `@=0` is invalid.
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Problematic characters (space, `=`, `#`, `;`) can be written as Unicode codepoints `U+xxxx`.
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* a line like `a-z=<xx>` is equivalent to lines `a=<xx>`, `b=<xx+$01>` all the way to `z=<xx+$19>`.
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* a line like `KATAKANA=>DECOMPOSE` means that katakana characters with dakuten or handakuten
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should be split into the base character and the standalone dakuten/handakuten.
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* similarly with `HIRAGANA=>DECOMPOSE`.
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* lines like `{<escape code>}=<xx>`, `{<escape code>}=<xx><xx>` etc.
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define escape codes. It's a good practice to define these when possible:
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`{q}`, `{apos}`, `{n}`, `{lbrace}`, `{rbrace}`,
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`{yen}`, `{pound}`, `{cent}`, `{euro}`, `{copy}`, `{pi}`,
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`{nbsp}`, `{shy}`.
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