fix pod errors "alternative text ... contains non-escaped | or /"

these were visible e.g. on metacpan:

    1 POD Error
    The following errors were encountered while parsing the POD:
    Around line 374:
    alternative text 'filter/filters' contains non-escaped | or /
    alternative text 'constraint/constraints' contains non-escaped | or /
    alternative text 'inflator/inflators' contains non-escaped | or /
    alternative text 'validator/validators' contains non-escaped | or /
    alternative text 'transformer/transformers' contains non-escaped | or /