* Permit Date/Time Entered on Spreadsheet to be Calculated as Float
Fix#1416. I do not entirely understand the use case for this old issue, but resolving it seems straightforward. Issue complains that user-entered date/time fields may be interpreted as either float or int when PhpSpreadsheet reads them. Issue suggests getCalculatedValue treat all date/time fields as float; that seems like a breaking change. However, adding an option to permit it seems okay. That option might be implemented as either a property of Calculation, or a static property of Cell. Since the changed logic is found in Cell (and Shared/Date), I opted for the latter.
In Cell, the property `$parent` is incorrectly described in doc block as `Cells`, and should be `?Cells`. This change eliminates some Phpstan and Scrutinizer problems, and should allow the elimination of some try/catch blocks - I have not done an exhaustive search for those.
Calls to `isDateTime` could have affected activeSheet and selectedCells; they no longer can. Optional parameters are added to it and the functions it calls to accommodate the new functionality; the defaults for the new parameters will, of course, return the same result as the earlier versions of the functions would have returned.
* Scrutinizer - Self-inflicted
Tests used constant which I deprecated.
* Document calculation caching; and how to disable it and how to flush the cache
* Quoted text for string values beginning with `=`, so that they are still treated as strings and not as formulae
* Warning about assigning cells to variables
* Further warning about assigning cells to variables
The \PhpOffice\PhpSpreadsheet\Shared\Date class has support for setting an alternate timezone which affects the conversion of Excel Date timestamps in PhpSpreadsheet. This amendment is an effort to document this support.
We wrapped lines to make easier the source easier to read, and to have more manageable diffs.
This was done with something like:
```sh
pandoc --wrap=auto --atx-headers -f markdown -t markdown-fenced_code_attributes+pipe_tables+raw_html+intraword_underscores`
```
We aim for long pages instead of several small one, to make
`CTRL+F`ing easier and URL less prone to changes in the future.
There is still way to improve it though...
oleibman
MarkBaker
CoryHrycko
Adrien Crivelli
Mark Baker
Jon Dufresne
netpassprod1
Paul Klimov