Rendering can be suboptimal because there is no default/fallback css loaded.
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The tlig feature
In TEX it is still common to use two keyboard dashes to obtain an en-dash. An en dash is used to indicate a number range, e.g., 1785--1906.
In TEX it is still common to use three keyboard dashes to obtain an em-dash. An em-dash is used to indicate a prominent parenthesis---in modern usage the en-dash is becoming more popular for this task---as well as between the end of an epigraph and its author.
In CONTEXT there is a dedicated control sequence for the en-dash. An en-dash is used to indicate a number range, e.g., 1785–1906.
In CONTEXT there is a dedicated control sequence to obtain an em-dash. An em- dash is used to indicate a prominent parenthesis—in modern usage the en-dash is becoming more popular for this task—as well as between the end of an epigraph and its author.