Merged Cells not parsed if in "readonly" mode

[MattInventPartners]

Took me quite a while to find this one.

In Reader/Xlsx.php, we have the following:

Line 877: if ($xmlSheet && $xmlSheet->mergeCells && $xmlSheet->mergeCells->mergeCell && !$this->readDataOnly) {

The net effect is that if the sheet is opened in "readonly" mode, it won't find any of the mergedCells, and other methods such as:

cell::isInMergeRange()
cell::isMergeRangeValueCell()
cell::getMergeRange()

...incorrectly return false for merged cells.

[MarkBaker]

That's because the "structure" of the spreadsheet isn't data; so it depends on your definition of "incorrectly". readDataOnly only loads the data that's contained in the spreadsheet cells, not the "structure" of the spreadsheet, or the styles.