Dots (.) are valid characters within most modern file names across Windows, macOS, and Linux systems. While a dot is typically used to separate the main part of the filename from its extension (like "report.txt"), you can also place dots anywhere else within the name itself ("project.backup.notes.docx" or "photo.2024.July.vacation.jpg"). It serves purely as a character within the name structure at these points and does not signify an extension break unless positioned as the final separator before the extension.

For example, developers often include dots in file names to indicate versions or stages, such as "documentation.draft.v1.pdf". Photo management systems frequently use dots in filenames automatically generated from timestamps like "IMG_20240520.120045.jpg". Software packages or datasets might use extensive dot separators for hierarchical naming, e.g., "company.dataset.category.subset.csv".

A key advantage is increased organization and meaning within the name. However, potential confusion arises if dots are used inconsistently, as users or software might misinterpret parts before a dot as extensions. Some legacy systems (like older DOS-based programs) might still have restrictions on dots or filenames overall, but this is increasingly rare. Double extensions (e.g., "report.pdf.exe") can pose security risks, as the visible "pdf" might hide the executable ".exe" extension. Most environments now fully support internal dots.