Percent Yield Spread

[rf040234]

Can somebody explain this below?
Typical contraction of credit percent yield spreads during upward shifts of the benchmark yield curve does not necessarily signal an imminent bout of underperformance for the credit asset class.
The usual expansion of credit percent yield spreads during low rate periods overstates the risk as well as the comparative attractiveness of credit debt

 

[rf040234]

Any help would be greatly appreciated. Thanks.

 

[sparty419]

Where is this from?

 

[rf040234]

page 79 vol 4, under section “3. Percent Yield Spread Analysis”