Sometimes, especially in presentations, I want to tag a formula using a star rather than using a formula number. In LaTeX, this is easy. Just use \tag{...}
:
\begin{equation} a^2 + b^2 = c^2\tag{\ensuremath{\star}} \end{equation}
However, ConTeXt currently does not have any command that is equivalent to \tag
. I used to go through a log of hoops to get starred formulas. Today, I just realized the proper way to get them.
Instead of thinking in a adhoc manner like \tag{...}
think systematically. What will be the tag for the next formula. ★★ . And next. ★★★. And then? Using a string of stars soon becomes unbearable, so we have to use some other symbol. So, essentially, starred formulas are another way to number formulas. So, what I need is to specify how to convert numbers to symbols. Ah! ConTeXt has an option for that. I can get starred formulas by
using (in MkIV)
\defineformula[star][numberconversion=set 1]
or using (in MkII)
\defineformula[star][conversion=set 1]
This defines a \startstarformula ... \stopstarformula
that is similar to \startformula ... \stopformula
but uses set 1
conversion. set 1
is one of the predefined conversion functions in ConTeXt which is equal to {★ , ★★, ★★★, †, ††, †††,, *, **, ***}. Each symbol in the set is used cyclically as the formula “number”. Other predefined symbol conversions are

set 0
{•, – , ★, △, ○, medcircle, ◯, □} 
set 2
{*, †, ‡, **, ††, ‡‡, ***, †††, ‡‡‡, ****, ††††, ‡‡‡‡} 
set 3
{★ , ★★, ★★★, ‡, ‡‡, ‡‡‡, ¶, ¶¶, ¶¶¶, §, §§, §§§, *, **, ***}
If you want a different set of symbols, you can define your own conversion using
\defineconversion[myset][list of comma separated symbols]