Fix#4092. Change default value for Csv Reader autodetect line endings. Prior behavior can be enabled via `setTestAutodetect(true)`.
Change default value for Html Writer "better boolean" logic. Prior behavior can be explicitly enabled via `setBetterBoolean(false)`.
Change default for Xlsx Writer forceFullCalc option. Prior behavior can be explicitly enabled via `setForceFullCalc(null)`.
Fix#4311. Excel applies Conditional Formatting rules according to a priority specified in the xml. The priority must be a natural number; the rules are applied in order from lowest priority number to highest. When reading an Xlsx spreadsheet, PhpSpreadsheet has been ignoring the priority, which can result in differences from Excel's behavior, especially when CF cell ranges overlap (note that overlapping ranges are not supported in Xls format).
If an application uses PhpSpreadsheet to add new Conditional Formatting to a worksheet and does not change its priority from the default (0), the Xlsx Writer will assign a priority with a higher value than any of the CF objects which have been assigned a priority (either from reading it or explicitly assigning it).
Fix#4248. PhpSpreadsheet has used what appear to be default attributes and tags when they are missing from Fill patterns and colors. However, Excel handles their absence a little differently from what the "default" would require. PhpSpreadsheet is changed to omit the attributes and tags in question when missing. This change is mostly targeted towards Xlsx read and write, but minor changes for Xls and Html write are also included.
This seems like it could be a breaking change, but I don't think it is. One test (DefaultFillTest introduced by PR #2050) must change, but the change is internal - loading and then saving the spreadsheet used in that change will appear the same after this change as it did before. Other differences are very likely to be bug fixes rather than breaks.
oleibman