R5RS requires that Scheme support five indicators for the precision of floating-point values, not only the default e but also s, f, d, and l. Only a few Schemes actually support more than one precision, so this is mostly noise. Shall we make it an optional feature?
There's nothing in particular to change here - the standard already states:
Although Scheme allows a variety of written notations for numbers, any particular implementation may support only some of them.
I considered making the optionality more clear in the section on precision indicators, but it already uses "may" for everything. But it's a lot of text for something almost all implementations ignore - suggestions welcome.
The "may"s in 6.2.4 are not RFC 2119; they express what the user can do to achieve a certain result. Since the purpose of a standard is to define the agreement between users and implementers, the whole thing should be recast in terms of what implementations MUST, SHOULD, or MAY do. I just filed a ticket for RFC 2119 compliance.
Here's my suggestion:
In systems with inexact numbers of varying precisions it may be useful to specify the precision of a constant. For this purpose, implementations MAY accept numerical constants written with an exponent marker s, f, d, or l in place of e. The effect of these markers is implementation-defined.
The WG voted to make the precision indicators optional.