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01-uids.mdwn
[[!meta title=“2.1 | Uids”]]
Uids
Resources are represented by Unique Identifiers - Uids - which are by themselves meaningless, and should generally be random and generated by a computer. It’s possible in Idan to specify them directly in the document. They may also appear directly if a document has been processed by software, and Uids were automatically generated and inserted into the text.
The recommended scheme for Uids is generating them as version 4 UUIDs. This is the version of UUID that is randomly generated and isn’t based on time, location or system information.
A Uid is a string of Graphical Unicode characters with no whitespace. It is written with angle brackets (< and >) surrounding it. For example:
<b3742023-97ef-4fb0-9dd2-4582d946d6f1>Since Uids can technically contain >, it’s possible in Idan to include a > inside a Uid by putting a backslash before it. In other words, \> is an escape sequence which means >. Any use of \ as-is in a Uid is treated as an escape sequence. To specify \ directly, escape it too, i.e. \\ means \. For example, the following literal expresses the Uid 123<456>789\0>123\\45:
<123<456\>789\\0\>123\\\\45>Each > and \ is preceded by the escape sequence marker \.
There is another special case: the form <%> is used as a generator, explained in the section about placeholders. Since % is technically a valid Uid, Idan allows to specify it as <\%>. Note that in any other Uid which contains %, the sequence \% is invalid. For example, <123\%456> isn’t a valid Uid literal. If the Uid 123%456 was meant, it should be written as <123%456>, without the backslash. If the Uid 123\%456 was meant, then the \ should be escaped: <123\\%456>.