Why does ConTeXt sometimes ignore surrounding font properties?

Question

I am working on a document which contains a wide range of font styles and sizes. I am using commands such as \ss to change to sans serif, \tfa to set the font size to size "a", and \bf to make text boldface. I am also using brackets to define which areas receive which formatting.

I found the behavior is sometimes unpredictable. Here is an example:

\starttext
    {\ss
        This is 12pt sans serif text. \crlf
        {\tfc This is 20.7pt sans serif text.} \crlf
        {\bf
            This is 12pt bold sans serif text. \crlf
    {\tfc This is 20.7pt bold sans serif text.} \crlf
    {\tfc \bf This is 20.7pt bold sans serif text.} \crlf
        }
     }
     This is 12pt serif text.
\stoptext

In this example, \ss from line 2 sets all text within the brackets to sans serif, however, the \bf command in line 5 does create boldface text in line 7.

Why is the text on line 7 ignoring the \bf command on line 5?

Answer 1

Both \bf and \tf are font alternatives. So, only one can be active at a time. If you just want to scale according to a, b, c values, use:

\unprotect
\unexpanded\def\setbodyfontscale#1%
    {\font_helpers_set_current_font_size{#1}\the\everybodyfont}
\protect

\setbodyfontscale{c}