Linked just after the paragraph you quoted, it links to this blog post. In that page, it's stated that:
We’ve been doing a lot of work to understand the impact of voltage and temperature on lifetime, and are now able to offer a “turbo mode”, which dynamically enables overclock and overvolt under the control of a cpufreq driver, without affecting your warranty.
So long as you don't set
force_turbo, which forces turbo mode to run even when not necessary, the warranty void bit will likely not be set. This is confirmed by one of the engineers at the Foundation, who states:
Note, that overclocking through raspi-config doesn't set your "warranty" bit. What sets the warranty bit now, is:
(force_turbo || current_limit_override || temp_limit>85) && over_voltage>0
So, if you are manually overclocking and want to know what is "allowed", then stick to those config.txt options.
If you've already blown your warranty bit, or don't care, then feel free to change anything.
In practice, this means you're limited to a 1.35 V core voltage, because without
current_limit_override, you can only set
over_voltage to a maximum of 6.