Returns the numerical value it can extract from a given string
Implemented by: dartmouth5, decbasic, altair8K, Applesoft, TI994, CBM, Atari, msatari, level2, trscolor, colormc, spectrum, BBC, GWBASIC, MSX, bwbasic, bw32, QBasic, VBDOS, FreeBASIC, ugBASIC, minibasicmm, minibasicjs
With variations: Gambas
Also written as: