About the behavior of iOS 10.3 and higher.

[kirou]

There is a problem with iOS 10.3 or later terminal.

https://github.com/readium/readium-shared-js/blob/master/js/views/reflowable_view.js#L315
When this process is confirmed at iOS 10.2 or less, it becomes vertical-rl, and if it checks at iOS 10.3 and above it becomes horizontal-tb and the result will be different.

https://github.com/readium/readium-shared-js/blob/master/js/views/reflowable_view.js#L307
The result was different between getComputedStyle itself, iOS 10.2 and iOS 10.3.
Therefore, I think that the result differs also with getPropertyValue.

Have you heard the story that the same phenomenon occurred?

[danielweck]

For reference:

 var htmlBodyComputedStyle = win.getComputedStyle(_$htmlBody[0], null);
        if (htmlBodyComputedStyle)
        {
            _htmlBodyIsLTRDirection = htmlBodyComputedStyle.direction === "ltr";

            var writingMode = undefined;
            if (htmlBodyComputedStyle.getPropertyValue)
            {
                writingMode = htmlBodyComputedStyle.getPropertyValue("-webkit-writing-mode") || htmlBodyComputedStyle.getPropertyValue("-moz-writing-mode") || htmlBodyComputedStyle.getPropertyValue("-ms-writing-mode") || htmlBodyComputedStyle.getPropertyValue("-o-writing-mode") || htmlBodyComputedStyle.getPropertyValue("-epub-writing-mode") || htmlBodyComputedStyle.getPropertyValue("writing-mode");
            }
            else
            {
                writingMode = htmlBodyComputedStyle.webkitWritingMode || htmlBodyComputedStyle.mozWritingMode || htmlBodyComputedStyle.msWritingMode || htmlBodyComputedStyle.oWritingMode || htmlBodyComputedStyle.epubWritingMode || htmlBodyComputedStyle.writingMode;
            }

            if (writingMode)
            {
                _htmlBodyIsLTRWritingMode = writingMode.indexOf("-lr") >= 0; // || writingMode.indexOf("horizontal-") >= 0; we need explicit!

                if (writingMode.indexOf("vertical") >= 0 || writingMode.indexOf("tb-") >= 0 || writingMode.indexOf("bt-") >= 0)
                {
                    _htmlBodyIsVerticalWritingMode = true;
                }
            }
        }