htmlspecialchars call in template.php needs to be update

[khaihong]

Under wp-admin/includes/, the call needs to be changed from
htmlspecialchars($context))
to
htmlspecialchars($context, $flags=NULL, $encoding='UTF-8'))

Otherwise, there are constant debug warnings:
htmlspecialchars(): charset not supported, assuming utf-8

I've had those warnings for themes twenty-fourteen and twenty-seventeen, using only 2 active plugins Query Monitor and Really Simple SSL.

[johnbillion]

Thanks for the report, @khaihong! Welcome to WordPress Trac.

It looks like this warning is coming from the do_meta_boxes() function. The $context parameter should be escaped with esc_attr() instead of htmlspecialchars().

[abdullahramzan]

Please consider this one.

[SergeyBiryukov]

esc_attr() accepts 1 parameter, not 3.

[leanderiversen]

Like @SergeyBiryukov mentioned, esc_attr() only accepts 1 parameter.

[johnbillion]

In 43365:

Options, Meta APIs: Use the correct escaping function when outputting the meta box context.

Props khaihong, abdullahramzan, leanderiversen, aryamaaru, lbenicio, palmiak

Fixes #44274

[johnbillion]

In 43366:

Options, Meta APIs: Use the correct escaping function when outputting the meta box context.

Props khaihong, abdullahramzan, leanderiversen, aryamaaru, lbenicio, palmiak

Fixes #44274

Merges [43365] to the 4.9 branch.