Its defaults are to unescape within single quotes, and escape within double quotes and here-docs. Right now, it leaves everything as-is, which means our code is inconsistent and need not be. Further, although dealing with complex regular expressions will never be easy, I find it much easier to figure out what's going on when superfluous back-slashes are removed.
These changes were all made automatically using the "fix" script, so should be reliable. They, of course, pass all unit tests.
Fix#4319. PR #3495 allowed Mpdf and Tcpdf to handle hidden rows and columns. The handling is a little off when merged cells are part of the output. The fix for Mpdf is pretty straightforward. Tcpdf is a little more convoluted. Dompdf and Html do not require a change. Unit tests are added for the same scenario for all of Mpdf, Tcpdf, Dompdf, and Html.
Fix#3557. Borders around merged cells are not handled correctly for Mpdf. Although a perfectly acceptable workaround is suggested in the issue, it would be better if things just worked without the workaround. Html and Dompdf work with the existing code. As it turns out, Tcpdf does not work, but for a different reason than Mpdf.
Mpdf was not working because Mpdf does not honor the `!important` attribute in Css. We can get it working almost perfectly by suppressing `border*:none`; the exception is fairly Byzantine, and I'll be glad to discuss the matter should anyone report a problem with it. At any rate, it's not working now in the exception case, so we won't be any worse off.
Tcpdf was not working because the merging of attributes happened only when `useInlineCss` was not being used, but Tcpdf does use it. Merging of border attributes is now added for useInlineCss.
Tcpdf issues warnings when processing hidden rows. Some time ago, Mpdf was having problems in the same situation; this was resolved by not writing out hidden rows in the html which Mpdf uses to generate its file. The same solution can be easily applied to Tcpdf.
Neither Tcpdf nor Mpdf handles hidden columns. Dompdf doesn't have a problem with either rows or columns. At any rate, the solution for Tcpdf/Mpdf is to not write out the data in the hidden columns. It is more difficult to implement this for columns than for rows, but this PR should do the trick.
Html writer generally uses `display:none` for the data in suppressed columns. This works, but is technically incorrect - the "approved" method is `visibility:collapse` on the col element. However, Firefox doesn't handle that correctly (open bug was filed over a decade ago), and, since all browsers seem to handle the existing implementation, it is left alone.
Among other considerations, this PR is a necessary precursor for supporting printArea in Html/Pdf should we decide to do that (issue #3941).
Writer/Html protected property `$isMPdf` is deprecated with this PR in favor of testing for `instanceof Mpdf`.
oleibman