You can disable many validator messages that you don't want to see, though not all messages can be disabled.
The numbers in square brackets that appear in front of some of the validator messages (like "") refer to flags that can be turned off (disabled) or turned on (enabled). By default, all flags are enabled. If you see a message that you do not want to see anymore on all future validations, then you can bring up the context menu on that message and disable the flag (the context menu is usually shown by right-clicking the mouse on the validator message).
Disabling a flag will normally cause the message, as well as other related messages, to not appear again. You can always enable any flags that you disable by going to the Validator Engine Options. This capability is a powerful customization feature of CSE HTML Validator Std/Pro and is not included in the free lite edition.
Most messages can be individually disabled. Unlike disabling a flag, which may cause many related messages to be disabled as well, disabling a message on an individual basis will not affect other messages. To disable an individual message, bring up the context menu on the message and choose Message Options->Disable using Message ID or Message Options->Disable using Exact Text Match. Note that there may be other options as well, such as changing the message type. Most, but not all, messages can be controlled like this.
Learn more about disabling validator messages.