Partial covering convolution model

The new release will include a partial covering convolution model (partcov) which can be used to turn any absorption model into a partially covered version. This depends on the new model parsing that takes into account the non-associative nature of convolution models. So, if P is the partial covering model, M the multiplicative absorption model and A the additive model then (PM)A turns M into a partial covering absorption. However PMA or P(MA) applies the partial covering the product of M and A which does not give the desired result.