Emphasis in GitHub Flavored Markdown

GFM_emphasis_summary.md

Emphasis in GitHub Flavored Markdown

Emphasis begins and ends according to 17 rules in the specification, but here is a summary in three rules:

1. Use either asterisks or underscores to emphasize a character next to a space, punctuation, or the beginning or end of a line. Put an emphasis mark immediately next to a character, with no space between, as in _this!_ for this!

   • Exception. Special punctuation marks override this rule, including a backslash (\), backtick (`), and square brackets ([ ]) which cause an asterisk or underscore to be rendered as a character and ignored as an emphasis mark.

2. Use an asterisk to emphasize letters and numbers next to letters and numbers, as in *as*terisk for asterisk. By contrast, an underscore is not an emphasis mark between letters and numbers, as in not_italic.

3. To emphasize punctuation next to letters and numbers, use HTML tags, as in this<em>!</em> for this! By contrast, an asterisk and underscore cannot emphasize punctuation next to an unemphasized letter or number.

Test cases

Emphasized	Next to	Underscores	Asterisks	Raw underscores and asterisks
Letters	Spaces	r italic r	r italic r	r _italic_ r *italic* r
"	Letters	L_regular_L	LitalicL	L_regular_L L*italic*L
"	Numbers	1_regular_1	1italic1	1_regular_1 1*italic*1
"	Punctuation	!italic!	!italic!	!_italic_! !*italic*!
Numbers	Spaces	r 11italic11 r	r 11italic11 r	r _11italic11_ r *11italic11* r
"	Letters	L_11regular11_L	L11italic11L	L_11regular11_L L*11italic11*L
"	Numbers	1_11regular11_1	111italic111	1_11regular11_1 1*11italic11*1
"	Punctuation	!11italic11!	!11italic11!	!_11italic11_! !*11italic11*!
Punctuation	Spaces	r !!italic!! r	r !!italic!! r	r _!!italic!!_ r *!!italic!!* r
"	Letters	L_!!regular!!_L	L*!!regular!!*L	L_!!regular!!_L L*!!regular!!*L
"	Numbers	1_!!regular!!_1	1*!!regular!!*1	1_!!regular!!_1 1*!!regular!!*1
"	Punctuation	!!!italic!!!	!!!italic!!!	!_!!italic!!_! !*!!italic!!*!