|Language and punctuation / Stem sentences, glue text, and other transitional information|
Stem sentences cannot be used to introduce steps in a task topic. The topic title provides sufficient context for the user to understand the purpose of the procedure.
The DITA task information task doesn't have a dedicated element for a stem sentence to introduce the steps. The assumption that can be drawn is that a stem sentence (eg, "To change the wheel, proceed as follows") is not required. A descriptive topic title will obviate the need for a stem sentence, particularly when used in conjunction with a carefully crafted short description.
Do not break the semantics of your content by trying to force a stem sentence into a structure where it is not clearly permitted. For example, do not include a stem sentence as the last paragraph in the context element, using the logic that it will be rendered immediately before the step block.
The DITA Technical Committee did not forget to include a stem sentence element. It was deliberately not included, after careful consideration and consensus amongst the committee members.