Displayed equations in (AMS-)LaTeX is well documented and widely understood. Sometimes, however, one wants to have displayed textual conditions in mathematical writings. This is seen in the following image (from Hodges's Model Theory):
Here (5.12) is a displayed formula that we all know well, whereas (5.13) is what I am trying to describe. It appears that lines like (5.13) have different spacings than genuine displayed formulas like (5.12).
What is the standard mechanism in (AMS-)LaTeX to be used to display conditions like (5.13)? Not only does a math environment solely containing \text seem idiotic, but also it violates the principle of semantic mark-ups: lines like (5.12) are just some prose displayed differently, not mathematical symbols (albeit the former may contain the latter).
Addendum: another opposition toward usual equation commands + \text is that they cannot handle line breaks automatically. With genuine equations manual line breaks pose no issue (though cumbersome), but with prose the line breaks must look the same as elsewhere.
\texthere is it is for textual comments in displayed math. Note I would write it as\text{$A$ is $I'$-injective ...}– daleif Jan 03 '23 at 11:04equationas it is a displayed thing numbered as an equation, then\textbecause it is text. – David Carlisle Jan 03 '23 at 12:49\parbox. Small graphics can also be set in this manner. When the textual context makes sense to do this, it is not inappropriate. – barbara beeton Jan 03 '23 at 17:41