Fix data validation issues (#975)

* Fix `SetDropList` to allow XML special characters

* This closes #971, allow quotation marks in SetDropList()

This patch included a XML entity mapping table instead of
xml.EscapeText() to be fully compatible with Microsoft Excel.

* This closes #972, allow more than 255 bytes of validation formulas

This patch changed the string length calculation unit of data
validation formulas from UTF-8 bytes to UTF-16 code units.

* Add unit tests for SetDropList()

* Fix: allow MaxFloat64 to be used in validation range

17 decimal significant digits should be more than enough to represent
every IEEE-754 double-precision float number without losing precision,
and numbers in this form will never reach the Excel limitation of 255
UTF-16 code units.

1 files changed, 6 insertions, 0 deletions

diff --git a/errors.go b/errors.go
index 4931198..6b32563 100644
--- a/errors.go
+++ b/errors.go
@@ -105,4 +105,10 @@ var (
 	ErrSheetIdx = errors.New("invalid worksheet index")
 	// ErrGroupSheets defined the error message on group sheets.
 	ErrGroupSheets = errors.New("group worksheet must contain an active worksheet")
+	// ErrDataValidationFormulaLenth defined the error message for receiving a
+	// data validation formula length that exceeds the limit.
+	ErrDataValidationFormulaLenth = errors.New("data validation must be 0-255 characters")
+	// ErrDataValidationRange defined the error message on set decimal range
+	// exceeds limit.
+	ErrDataValidationRange = errors.New("data validation range exceeds limit")
 )