Before revision:  The null hypothesis is that breaks in different parameters (either regression coefficients or elements of the covariance matrix of the errors) occur at a common locations or are separated by some positive fraction of the sample size  . Under the alternative hypothesis, the break dates  are not the same and also need not be separated by a positive fraction of the sample size across parameters .
After revision:  The null hypothesis is that breaks in different parameters occur at common locations and are separated by some positive fraction of the sample size . Under the alternative hypothesis, the break dates are not the same and also need not be separated by a positive fraction of the sample size across parameters .