The Context communication info parameter must be filled with any static text as a required field. The value resolver only returns values from communication information whose 'context' (communicationContext) matches the value specified here exactly (incl. upper/lower case).

►NOTE◄ Since the parameter cannot be left 'empty', the value resolver categorically does not consider communication information without context.

The optional User parameter allows a single selection from the Users list. As can be seen in the image, the Combobox element supports a search function.

If no user is selected, then the evaluation refers to the Current user valid in the context of the value resolver, unless it is a guest user.

►IMPORTANT◄ During configuration, only users with read-only access at the minimum in the current session appear in the drop-down list. If an existing configuration refers to a user for whom there is no read access in the current session, the label appears as 'hidden – User'. At runtime, read access is irrelevant for the configuration behaviour.

The association criteria is configured as shown on the right:

• The external Entity property rule uses the Is empty comparison type in conjunction with a negation to determine whether the contained concatenation of value resolvers has found an 'acceptable' e-mail address in the logged-in user's account. This evaluation determines whether the association criteria is considered 'passed' or 'failed'.

• Within the concatenation, the Mail address user value resolver is first used to search for e-mail addresses for the context registration in the address of the logged-in user (the User parameter remains empty). If such communication information exists, the value resolver passes its values to the concatenated successor as a list of strings.

• The concatenated Rule list resolver checks the 'E-mail addresses' – if a list is passed and not 'no value' (null) – with another Entity property rule, which is shown in more detail in the following section. Since the Resolve all as list option is not selected, the search stops at the first 'match' and returns it, so the external Entity property rule is 'non-empty' and the association criteria is considered to have 'passed'.

• If no relevant communication information is found, or none of the e-mail addresses entered there passes the formal test described below, the association criteria is considered to have been 'failed'.

►NOTE◄ If the Current user in the execution context of the value resolver refers to a guest user (see Guest users), the Mail address user value resolver always returns 'no value' (null). Then the association criteria is considered as 'failed'. So the configured rule implies the check if a 'full' user is considered as Current user.

The image on the right shows in detail the Rule list resolver configured for the example:

• On the left side of the Entity property rule, the list value to be checked – the supposed e-mail address – is subjected to a two-step text substitution, which serves to replace a text that is evaluated as an 'acceptable' value for an e-mail address with the randomly chosen string @EMAIL@. The Equals comparison type checks against the same string (see the static text on the right).
  
  

• A special case where this string @EMAIL@ was specified directly in the user account instead of a valid e-mail address is handled by the first Replace text value resolver (left), which replaces this text with an empty string.

• The concatenated second Replace text value resolver uses a 'regular expression' as Search text, which completely replaces the text with the 'keyword' @EMAIL@ if it matches the desired check criteria for the e-mail.

►NOTE◄ The regular expression used as the Search text in the example is deliberately crude and therefore 'fallible' as far as the distinction between acceptable and unacceptable e-mail addresses is concerned. It can be replaced by any custom expression that covers specific requirements more precisely. In particular, control over the characters allowed to be used for the username and domain between the required components ('@' and '.') should be stricter. Currently, only spaces ('\s') and the @ symbol ('@') are excluded.