To collect the number of comments users posted to a website page, what feature would be used?

In Google Analytics, to collect quantitative data such as the number of comments users have posted on a webpage, the appropriate feature to use would be a custom metric. Custom metrics are specifically designed to capture data points that are numerical in nature, allowing you to track values that matter to your business objectives, such as the number of comments.

Custom dimensions, while important for capturing descriptive attributes about the user or their interactions, are not suited for quantitative measurements. They can store information like user roles or categories but do not sum or count values like comments. Custom filters help refine and segment data rather than collect it. Lastly, custom alerts serve to notify users when specific conditions in the data are met but do not directly collect or store new data types.

Using custom metrics gives you the flexibility to define what you want to measure and ensure the accuracy of your analytical insights related to user interactions, such as comments.