File-system check types validate filename and path conventions for items.

Check types in this family:

• Extension in: Allow only specific file extensions.
• Index file required: Require that every directory containing items has an index file.
• Name affix: Require a name to start with a prefix and/or end with a suffix.
• Name case: Require a name (or path segments) to follow a case style.
• Name length: Bound the character length of a name.
• Name matches field: Require a name to equal a frontmatter field, optionally slugified.
• Name regex: Require a name to match a regular expression (anchored).
• Parent directory in: Require that the file’s parent directory name is in an allowed set.
• Parent directory matches field: Require the parent directory name to equal a frontmatter field.
• Path charset: Constrain the characters allowed in the item’s path.
• Path depth: Bound directory nesting relative to the collection root.
• Referenced files exist: Require path-valued frontmatter fields to resolve to real files.
• Unique filename: Require that no two items in the collection share a basename.