(1) -> )set output algebra on

T1:=hconcat("abc",vconcat([1,1234,123,12])$OutputForm)

   (1)  "abc" 1
             1234
             123
              12

(1)

output(T1::TEX)$OutputPackage

   ["$$", "\verb#"abc"#{\begin{array}{c}1\\{1234}\\{123}\\{12}\\\end{array}} ",
    "$$"]

T1 pretend SExpression

   (3)  (CONCAT ""abc"" (VCONCAT 1 1234 123 12))

(2)

In the following although the OutputForm? is apparently the same for each of "center", "right" and "left", the actual output generated by the "algebra" output is different. How can this be?

C1:=center(T1)

   (4)                                    "abc" 1
                                               1234
                                               123
                                                12

(3)

output(C1::TEX)$OutputPackage

   ["$$", "\mbox{\rm } ",
    "{\verb#"abc"#{\begin{array}{c}1\\{1234}\\{123}\\{12}\\\end{array}}} ",
    "$$"]

C1 pretend SExpression

   (6)
   (CONCAT  "                                  "
    (CONCAT ""abc"" (VCONCAT 1 1234 123 12)))

(4)

R1:=right(T1)

   (7)
                                                                       "abc" 1
                                                                            1234
                                                                            123
                                                                             12

(5)

output(R1::TEX)$OutputPackage

   ["$$", "\mbox{\rm } ",
    "{\verb#"abc"#{\begin{array}{c}1\\{1234}\\{123}\\{12}\\\end{array}}} ",
    "$$"]

R1 pretend SExpression

   (9)
   (CONCAT
    "                                                                    "
    (CONCAT ""abc"" (VCONCAT 1 1234 123 12)))

(6)

L1:=left(T1)

   (10)
   "abc" 1
        1234
        123
         12

(7)

output(L1::TEX)$OutputPackage

   ["$$",
    "{\verb#"abc"#{\begin{array}{c}1\\{1234}\\{123}\\{12}\\\end{array}}} ",
    "\mbox{\rm } ", "$$"]

L1 pretend SExpression

   (12)
   (CONCAT  (CONCAT ""abc"" (VCONCAT 1 1234 123 12))
    "                                                                    ")

(8)

Note also how the SExpression? is formatted differently. So maybe there is something "hidden" in the SExpression?. Strange!

Ref.

)sh OutputForm

 OutputForm is a domain constructor.
 Abbreviation for OutputForm is OUTFORM 
 This constructor is not exposed in this frame.
 72 names for 96 operations in this domain.
------------------------------- Operations --------------------------------

 ?*? : (%, %) -> %                     ?+? : (%, %) -> %
 -? : % -> %                           ?-? : (%, %) -> %
 ?/? : (%, %) -> %                     ?<? : (%, %) -> %
 ?<=? : (%, %) -> %                    ?=? : (%, %) -> %
 ?=? : (%, %) -> Boolean               ?>? : (%, %) -> %
 ?>=? : (%, %) -> %                    ?SEGMENT : % -> %
 ?..? : (%, %) -> %                    ?^? : (%, %) -> %
 ?and? : (%, %) -> %                   assign : (%, %) -> %
 binomial : (%, %) -> %                blankSeparate : List(%) -> %
 box : % -> %                          brace : % -> %
 brace : List(%) -> %                  bracket : % -> %
 bracket : List(%) -> %                center : % -> %
 center : (%, Integer) -> %            coerce : % -> OutputForm
 commaSeparate : List(%) -> %          convert : % -> InputForm
 dot : % -> %                          elt : (%, List(%)) -> %
 empty : () -> %                       ?exquo? : (%, %) -> %
 hconcat : (%, %) -> %                 hconcat : List(%) -> %
 hspace : Integer -> %                 infix : (%, %, %) -> %
 infix : (%, List(%)) -> %             infix? : % -> Boolean
 int : % -> %                          int : (%, %) -> %
 int : (%, %, %) -> %                  label : (%, %) -> %
 latex : % -> String                   left : % -> %
 left : (%, Integer) -> %              matrix : List(List(%)) -> %
 message : String -> %                 messagePrint : String -> Void
 not? : % -> %                         ?or? : (%, %) -> %
 outputForm : Integer -> %             outputForm : String -> %
 outputForm : Symbol -> %              over : (%, %) -> %
 overbar : % -> %                      overlabel : (%, %) -> %
 paren : % -> %                        paren : List(%) -> %
 pile : List(%) -> %                   postfix : (%, %) -> %
 prefix : (%, List(%)) -> %            presub : (%, %) -> %
 presuper : (%, %) -> %                prime : % -> %
 print : % -> Void                     prod : % -> %
 prod : (%, %) -> %                    prod : (%, %, %) -> %
 ?quo? : (%, %) -> %                   quote : % -> %
 rarrow : (%, %) -> %                  ?rem? : (%, %) -> %
 right : % -> %                        right : (%, Integer) -> %
 root : % -> %                         root : (%, %) -> %
 rspace : (Integer, Integer) -> %      scripts : (%, List(%)) -> %
 semicolonSeparate : List(%) -> %      slash : (%, %) -> %
 sub : (%, %) -> %                     sum : % -> %
 sum : (%, %) -> %                     sum : (%, %, %) -> %
 super : (%, %) -> %                   supersub : (%, List(%)) -> %
 tensor : (%, %) -> %                  vconcat : (%, %) -> %
 vconcat : List(%) -> %                vspace : Integer -> %
 zag : (%, %) -> %                     ?~=? : (%, %) -> %
 ?~=? : (%, %) -> Boolean             
 differentiate : (%, NonNegativeInteger) -> %
 dot : (%, NonNegativeInteger) -> %
 prime : (%, NonNegativeInteger) -> %

)sh OutputPackage

 OutputPackage is a package constructor
 Abbreviation for OutputPackage is OUT 
 This constructor is exposed in this frame.
------------------------------- Operations --------------------------------

 output : String -> Void               output : OutputForm -> Void
 outputList : List(Any) -> Void       
 output : (String, OutputForm) -> Void