DOI Namespace > Constraints on DOI Name Syntax in Specific Contexts

If the DOI name is used in specific application contexts then there may be requirements or restrictions on the use of particular characters:

•When presented as above as an URL (Uniform Resource Locator) with the web proxy address prepended, some characters must be percent encoded (for example, # must be encoded because this character is used in a URL to indicate the beginning of a URL fragment).

•Characters which cannot be handled directly in a specific network or reference context, or where ambiguity can arise (for example, minus sign, the hyphen, and the en-dash all look similar on the screen but carry different character values) should be avoided or encoded in an appropriate way (for example, for URLs: should be converted to UTF-8 and then hex-encoded).

The Unicode Standard imposes additional constraints on implementations of ISO/IEC 10646:2020, the Universal multiple-octet coded character set (usually referred to as the Universal Character Set, UCS). See Unicode for more information.