Clean up API docs for hook_file_mimetype_mapping_alter()

Thanks!

Our documentation standards currently require that when you refer to a class in documentation blocks, you include the full namespace of the class (starting with \ ), even in the text.

Other than that, it looks fine...

Minor fixes to remove extra space and better utilization of available space.

Looks good to me now, thanks! ... Well, we normally say hooks are "invoked" rather than "called". Want to clean that up?

+++ b/core/modules/system/system.api.php
@@ -2303,16 +2303,17 @@ function hook_install_tasks_alter(&$tasks, $install_state) {
 /**
  * Alter MIME type mappings used to determine MIME type from a file extension.
  *
- * This hook is run when file_mimetype_mapping() is called. It is used to
- * allow modules to add to or modify the default mapping from
- * file_default_mimetype_mapping().
+ * Called by \Drupal\Core\File\MimeType\ExtensionMimeTypeGuesser::guess(). It is

I'd also like to ask that this patch not be committed until #2299715: [meta] Move core hooks from system.api.php to core.api.php or other files is complete. That's a big patch and it's moving this hook.

Sure. Fixes as per #5.

Looks better, thanks! Again, I'd like to ask for this not to be committed until #2299715: [meta] Move core hooks from system.api.php to core.api.php or other files is dealt with, at which point this will need a reroll.

Ditto.

Never mind, the other patch already doesn't apply.

Committed d29adc8 and pushed to 8.x. Thanks!