I think it's anything which does a stringification.
DB<137> $x1 = (1.15*170)+0.50;
DB<138> p "$x1"
196
DB<139> p $x1
196
DB<140> printf "%.20f\n",$x1
195.99999999999997000000
DB<141> $str = $x1.""
DB<142> p length $str
3
DB<143>
yep!
DB<151> $x2 = (1.15*170)+0.50;
DB<152> Dump $x2
SV = NV(0x32cc698) at 0x32cc6b0
REFCNT = 1
FLAGS = (NOK,pNOK)
NV = 196
DB<153> p $x2
196
DB<154> Dump $x2
SV = PVNV(0x1cb938) at 0x32cc6b0
REFCNT = 1
FLAGS = (NOK,pNOK)
IV = 0
NV = 196
PV = 0x31a4748 "196"\0
CUR = 3
LEN = 32
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