Predicates on the step allow conditions to be specified.

They follow the step and are wrapped in square brackets ('[' and ']').

For example:

para[@id='mine']

selects 'para' elements where the 'id' attribute has value 'mine'.

There is a whole wealth of operators (including boolean logic) that can be used.

You can also have sub-expressions:

contents[para/@id='mine']

This selects a 'contents' element that has a child 'para' with an attribute 'id' of value 'mine'.