Explanation
The question is about referencing and using arrays of a CDT (Custom Data Type). The following statements are true:
* There is no difference between using "dot notation" and the index() function. Both methods can be used to access elements of an array by their position. For example, if a is an array of CDTs, then a[1] and index(a, 1) will return the same element.
* An array of integers can be passed as the second parameter to the index() function to return the data at those positions in the array. For example, if a is an array of CDTs, then index(a, {1, 3, 5}) will return an array of CDTs containing the elements at positions 1, 3, and 5 in a.
The following statements are false:
* Other Appian functions can be used within the square brackets "[]" when using dot notation to return specific data from the array. This is not possible, as dot notation only accepts integers or integer arrays as indices. For example, if a is an array of CDTs, then a[length(a)] will cause an error, as length(a) is not a valid index.
* The function wherecontains can act on operands of different types. This is not true, as wherecontains only works on operands of the same type. For example, if a is an array of CDTs and b is an array of integers, then wherecontains(a, b) will cause an error, as a and b are not of the same type.
References:
* Dot Notation
* index()
* wherecontains()

Explanation
The question is about choosing the right plug-in for a requirement that can only be achieved by using a plug-in. The following are three primary considerations in choosing the right plug-in:
* What are the compatible Appian versions? This is important because some plug-ins may not work with older or newer versions of Appian due to changes in APIs or features. You should check the plug-in
* documentation or release notes to see which Appian versions are supported by the plug-in.
* Is the plug-in Cloud-approved? This is important because some plug-ins may not be allowed in Appian Cloud environments due to security or performance reasons. You should check the Appian Cloud Approved Plug-ins list to see which plug-ins are approved for use in Appian Cloud.
* What are the limitations of the plug-in? This is important because some plug-ins may have known issues or limitations that could affect your requirement or use case. You should check the plug-in documentation or forums to see if there are any reported bugs or limitations for the plug-in.
The following are not primary considerations in choosing the right plug-in:
* What is the size of the plug-in? This is not a major factor, as plug-ins are usually small in size and do not affect the performance or storage of Appian significantly. However, you should still follow the best practices for managing plug-ins and avoid installing unnecessary or unused plug-ins.
* Who is the plug-in author? This is not a decisive factor, as plug-ins can be authored by Appian, third-party vendors, or community members. However, you should still consider the reputation and reliability of the plug-in author and check their support and update policies.
References:
* Plug-ins
* Appian Cloud Approved Plug-ins