A numeric value. Under this threshold, rather than showing the
p-value itself, show "< 1e-X" where X is the largest integer satisfying
this relationship.
alpha
The significance level.
star.symbol
A character to display next to those p-values that are
statistically significant (i.e., less then alpha).
html
A logical flag indicating whether to return HTML code or plain
text.
unicode.le
A logical flag indicating whether to use unicode
symbol U+2264
for "less-than-or-equal-to" (only applies when html is FALSE).