What does the source mean when it says 27 matters are necessary for valid prayer?

The 27 Requirements for Valid Prayer: Purity and Covering

• All 27 are external conditions that must exist before Takbir.
• The 27 are the total validity requirements and include both conditions and internal obligatory components.
• There are exactly 27 Sunnahs of prayer.
• The number refers only to purity rules.