* The number may have optional sign and digits after a decimal point, and may use exponential notation. Example: (-1.2e1, .0E+0, 1.e-3) => "Yes". As seen in the second and third number here, there may be no digits before or after the decimal point, but both at the same time (i.e., ".0" and "0." parse but not ".").
* If the number begins with "0x" or "0X" it is read in hexadecimal, where the digits a-f may be in either case. Hexadecimal notation must not be accompanied by decimal point, sign, or exponential notation.
* No whitespace is permitted within the numeral, even between the sign and the digits as in "+ 11", but both tabs and spaces may be used before and after the numeral without changing its value. In particular, by using a input of the form "1 " it is possible to make rectangular display empty while still parsing it as number. Note that pressing "Check" leads to the numbers being displayed in the rectangle in exactly the same way as they were displayed in the text box, which may depend on the position of the cursor in the text box.
ETA: Also, you mentioned rounding, but there is also exponent overflow and underflow. The application refuses to parse numbers greater or equal to 1.7976932e308. It parses arbitrary negative exponents fine, but it does not recognize that 1e-324 is greater than 0.
* The number may have optional sign and digits after a decimal point, and may use exponential notation. Example: (-1.2e1, .0E+0, 1.e-3) => "Yes". As seen in the second and third number here, there may be no digits before or after the decimal point, but both at the same time (i.e., ".0" and "0." parse but not ".").
* If the number begins with "0x" or "0X" it is read in hexadecimal, where the digits a-f may be in either case. Hexadecimal notation must not be accompanied by decimal point, sign, or exponential notation.
* No whitespace is permitted within the numeral, even between the sign and the digits as in "+ 11", but both tabs and spaces may be used before and after the numeral without changing its value. In particular, by using a input of the form "1 " it is possible to make rectangular display empty while still parsing it as number. Note that pressing "Check" leads to the numbers being displayed in the rectangle in exactly the same way as they were displayed in the text box, which may depend on the position of the cursor in the text box.
ETA: Also, you mentioned rounding, but there is also exponent overflow and underflow. The application refuses to parse numbers greater or equal to 1.7976932e308. It parses arbitrary negative exponents fine, but it does not recognize that 1e-324 is greater than 0.