\bfserieschanges the font weight to bold, so the following segment of code:
will appear in the typeset document looking like:
As can be seen, the font change only stays in effect until it
reaches the end of the group (signified by the closing curly brace
}.) For a command to be in the same
scope as another command, both commands must be within the same group.
For example, in the following,
\itshape are in the same scope:
But below, they are in different scopes:
Environments form an implicit scope.
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