Block assessment procedure for search cases requires a special return and tax on undisclosed income under revised rules. A new Chapter prescribes a special procedure for block assessment where a search or requisition occurs on or after the effective date: it defines the block period and undisclosed income, requires a single prescribed return for the block period, causes pending assessments for years in the block period to abate, sets rules for computation of aggregate block income and undisclosed income (with specified exclusions for certain international or domestic transaction evidence), prescribes time limits, authority levels, treatment of seized assets, and modified interest and penalty rules.