Because LATEX2e supports different encodings, definitions of commands for producing symbols, accents, composite glyphs, etc. must be defined using the commands provided for this purpose and described in. This part of the system is still under development so such tasks should be undertaken with great caution.
Also, |should be used for encoding-independent commands of this type. Note that it is no longer possible to refer to the math font set-up outside math mode: for example, neither |1| nor |2| are guaranteed to be defined in other modes.