HTML and CSS Reference
The variable is assigned a regular expression containing a decimal character \d ,
and followed by either one or zero literal periods, \.? . The question mark (zero or
one) controls the character preceding it, in this case a period. There is either one
period or no period at all in the string being matched.
The variable textString is assigned user input; in this example, 3.7 was entered.
The regular expression test method will return true because the string 3.7 matches
a decimal number, 3, followed by a period (or not one) and followed by another
decimal number, 7. See the examples in Figure 17.20.
Figure 17.20 The user entered 3.7 , or number, period, number (top); the user
entered 456 , or number, no period, number (middle); the user entered 5A6 , but
there must be at least two consecutive digits for a match (bottom).