Use numerical constants.

Performance optimization, but at cost of code clarity.
Revert "Use numerical constants."

This reverts commit db25de09f5dc931c0e2b31ce0ccdb58052f3105f.
Revert "Use integers instead of strings for tags."

This reverts commit ac611d51c9de9aa719b42b9463e6f28d6e7d74a4.