A method, comprising: providing, to a client device, configuration data specifying a set of whitelisted user interface elements of a publisher, each whitelisted user interface element being a user interface element from which content is eligible to be collected and transmitted from the client device; receiving, from the client device and for a user session in which a user interacted with one or more user interfaces of the publisher, event data including: interface data specifying a structure of the one or more user interfaces presented during the user session, user interaction data specifying user interactions with the one or more user interfaces, content of one or more first presented user interface elements that i) were presented by the one or more user interfaces and ii) match a whitelisted user interface element specified by the configuration data, wherein the client device does not provide non-whitelisted content of one or more second presented user interface elements that do not match a whitelisted user interface element specified by the configuration data, and a recorded size of an object that includes a block of text that is part of a user interface element of the one or more first presented user interface elements, wherein the user interface element includes both whitelisted and non-whitelisted content, and wherein the block of text includes the non-whitelisted content; and generating, based on the event data, playback of the user session that presents i) the one or more user interfaces, ii) the content of the one or more first presented user interface elements, iii) the user interactions with the one or more user interfaces, iv) for content of the one or more second presented user interface elements, a first masking element that represents the content of the second user interface element while masking actual content of the second user interface element, and v) for the user interface element that includes both the whitelisted and the non-whitelisted content, a second masking element with the size determined for the object that includes the block of text including the non-whitelisted content. providing, to a client device, configuration data specifying a set of whitelisted user interface elements of a publisher, each whitelisted user interface element being a user interface element from which content is eligible to be collected and transmitted from the client device; receiving, from the client device and for a user session in which a user interacted with one or more user interfaces of the publisher, event data including: interface data specifying a structure of the one or more user interfaces presented during the user session, user interaction data specifying user interactions with the one or more user interfaces, content of one or more first presented user interface elements that i) were presented by the one or more user interfaces and ii) match a whitelisted user interface element specified by the configuration data, wherein the client device does not provide non-whitelisted content of one or more second presented user interface elements that do not match a whitelisted user interface element specified by the configuration data, and a recorded size of an object that includes a block of text that is part of a user interface element of the one or more first presented user interface elements, wherein the user interface element includes both whitelisted and non-whitelisted content, and wherein the block of text includes the non-whitelisted content; and interface data specifying a structure of the one or more user interfaces presented during the user session, user interaction data specifying user interactions with the one or more user interfaces, content of one or more first presented user interface elements that i) were presented by the one or more user interfaces and ii) match a whitelisted user interface element specified by the configuration data, wherein the client device does not provide non-whitelisted content of one or more second presented user interface elements that do not match a whitelisted user interface element specified by the configuration data, and a recorded size of an object that includes a block of text that is part of a user interface element of the one or more first presented user interface elements, wherein the user interface element includes both whitelisted and non-whitelisted content, and wherein the block of text includes the non-whitelisted content; and generating, based on the event data, playback of the user session that presents i) the one or more user interfaces, ii) the content of the one or more first presented user interface elements, iii) the user interactions with the one or more user interfaces, iv) for content of the one or more second presented user interface elements, a first masking element that represents the content of the second user interface element while masking actual content of the second user interface element, and v) for the user interface element that includes both the whitelisted and the non-whitelisted content, a second masking element with the size determined for the object that includes the block of text including the non-whitelisted content.