[sjrosen]

When a patent or patent application is published, all the applications it claims priority to (e.g., provisional applications) become open for public inspection.

However, patent applications can act as prior art as of the day they are filed, which is often well before they are published. The justification for this is that, even though the information is not yet public, the applicant has established that they know that information and that it will be disclosed to the public when the patent publishes.

The question in Ariosa Diagnostics v. Illumina is whether the provisional application can also act as prior art as of its filing date. The court's decision was that only the material from the provisional application that was later claimed in the published patent counts as prior art as of the filing date. Everything else in the provisional application only counts as of the publication date.