Without the correct filename extension, macOS appears unable to associate files with apps, preview then using QuickLook, or index them for Spotlight. But there’s more to determining file types than extensions, there’s also a little magic involved.
QuickLook
Spotlight fails to index the content of text files starting with odd characters like ‘LG’ and ‘Draw’, Although we understand this is caused by checking the file type using file(1), this suggests an explanation of why it should do that. And whether it will ever get fixed for Intel Macs.
If generating QuickLook thumbnails and previews, and indexing metadata for Spotlight, depend on UTIs, how come they tolerate misleading file extensions? A simple practical demo.
How to discover what went wrong when a document doesn’t show the right thumbnail, but a generic icon instead. How to dive deeper to solve problems with 3rd party thumbnail and preview generators.
Generating icons for display as thumbnails, and previews of documents, depend on speed of delivery and icons as faithful as possible for their size. How QuickLook achieves this in Tahoe.
From the first image thumbnails around 35 years ago, the Mac has delivered better thumbnails and previews of documents, most recently using QuickLook. Here’s how it works, and how it can fail.
A summary of iCloud Drive syncing of attributes, data, extended attributes, document versions (complex), Spotlight index content, and QuickLook previews.
How to exclude folders and files from these services, with new problems apparent in macOS Tahoe over exclusions from Time Machine backups.
Why can’t some files be seen in thumbnails, or previews, but almost everything else can be seen thanks to QuickLook? And is this connected to Spotlight indexing?
The Preview pane in Finder windows can show a comprehensive list of metadata, or a shortened list you can customise in Preview Options. Here’s how to use it and how it can provide further information.
The Eclectic Light Company 