RealFloat package:text

Write a floating point value to a Builder.
Show a signed RealFloat value to full precision, using standard decimal notation for arguments whose absolute value lies between 0.1 and 9,999,999, and scientific notation otherwise.
Encode a signed RealFloat according to FPFormat and optionally requested precision. This corresponds to the show{E,F,G}Float operations provided by base's Numeric module. NOTE: The functions in base-4.12 changed the serialisation in case of a Just 0 precision; this version of text still provides the serialisation as implemented in base-4.11. The next major version of text will switch to the more correct base-4.12 serialisation.