Unless you have a one-off need to set a URL Alias, you can be assured that all aliases will be automatically applied to new content. Your website automatically generates URL/path aliases for various kinds of content (nodes, taxonomy terms, users) without requiring the user to manually specify the path alias.
In special cases where you do need a one-off Alias, simply deselect the Generate automatic URL alias checkbox and add your vanity URL in the text box provided prefixed with a forward slash.
Here is a list of the path patterns that will be applied to automatically generate URL aliases when content is created.
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