Data processing apparatus comprises a data memory; a selection controller comprising a computer processor; and a digital interface between a control process implemented by the selection controller and a text handling process implemented by the computer processor or another processor; in which: the selection controller is configured to provide a text document from the data memory to the text handling process to identify one or more characteristics of words in the text document; the selection controller is configured to provide user selection of one or more of the words in the text document to be substituted and of one or more target characteristics; and the selection controller is configured to request from the text handling process a set of one or more substitute words for the selected words such that the substitute words comply with the selected one or more of the target characteristics.