Syntax
Some tagging systems provide a single text box to enter tags, so to be able to tokenize the string, a separator must be used. Two popular separators are the space character and the comma. To enable the use of separators in the tags, a system may allow for higher-level separators (such as quotation marks) or escape characters. Systems can avoid the use of separators by allowing only one tag to be added to each input widget at a time, although this makes adding multiple tags more time-consuming.
A syntax for use within HTML is to use the rel-tag microformat which uses the rel attribute with value "tag" (i.e., rel="tag") to indicate that the linked-to page acts as a tag for the current context.
Read more about this topic: Tag (metadata)