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LaTeX: Why are digits allowed in environments, but forbidden in commands?

What exactly do csname and endcsname do?Why are some characters not allowed in command sequencesWhy does LaTeX make a distinction between commands and environments?Do all starred commands have anything in common?Why are some characters not allowed in command sequencesSuggestions for an automatic taxonomy environmentUse a character other than the backslash for commandsWhy are LaTeX macros so inconsistent?Are end… macro names reserved in LaTeX2e?Can't use command with square brackets in matrix environmentHow to control conditional statements within new commands and environmentsCreating Commands which Make New Environments

3

1

Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:

Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?

macros environments

share|improve this question

asked 7 hours ago

U. WindlU. Windl

1697

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You actually can use numbers in commands. If you do expandafterdefcsname mycommandwithanumber123456endcsname{} you'll define a command mycommandwithanumber123456. The environments are created using the csname...endcsname pair, so it's fine.
  
  – Phelype Oleinik
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.
  
  – Steven B. Segletes
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
  
  – U. Windl
  6 hours ago
  

  
  
  
  

add a comment | 

3

1

Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:

Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?

macros environments

share|improve this question

asked 7 hours ago

U. WindlU. Windl

1697

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You actually can use numbers in commands. If you do expandafterdefcsname mycommandwithanumber123456endcsname{} you'll define a command mycommandwithanumber123456. The environments are created using the csname...endcsname pair, so it's fine.
  
  – Phelype Oleinik
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.
  
  – Steven B. Segletes
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
  
  – U. Windl
  6 hours ago
  

  
  
  
  

add a comment | 

Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:

Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?

macros environments

share|improve this question

asked 7 hours ago

U. WindlU. Windl

1697

share|improve this question

asked 7 hours ago

U. WindlU. Windl

1697

share|improve this question

asked 7 hours ago

U. WindlU. Windl

1697

asked 7 hours ago

U. WindlU. Windl

1697

asked 7 hours ago

U. WindlU. Windl

1697

1 Answer
1

active

oldest

votes

7

The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.

This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.

environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).

So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.

share|improve this answer

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

add a comment | 

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7

The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.

This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.

environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).

So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.

share|improve this answer

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

add a comment | 

7

The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.

This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.

environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).

So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.

share|improve this answer

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

add a comment | 

The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.

This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.

environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).

So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.

share|improve this answer

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

share|improve this answer

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

edited 6 hours ago

Phelype Oleinik

24.9k54690

edited 6 hours ago

Phelype Oleinik

24.9k54690

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892

answered 6 hours ago

David CarlisleDavid Carlisle

497k4111441892