When certain relational operators are intersected, the resulting region set can be larger than the user anticipates. For example, the expression starts with R, ends with S matches every possible pair of R and S, even if other R's and S's occur in between. For situations where only adjacent pairs are desired, any relational operator can be modified by the keyword delimiter. For example, starts with delimiter S matches regions that start with some region matching S and overlap no other region matching S.