This site is a static rendering of the Trac instance that was used by R7RS-WG1 for its work on R7RS-small (PDF), which was ratified in 2013. For more information, see Home.
Ticket 118: Identifiers and representations of characters, booleans, number objects, and . must be explicitly delimited.
This means, for example, that #t#f, .10#f, #t.10, #\space25, etc. are all invalid lexical syntax.