[lex] Avoid "shall" when not stating a direct requirement

Author: lprv

source/lex.tex

@@ -104,15 +104,15 @@
 zero or more whitespace characters other than new-line followed by
 a new-line character is deleted, splicing
 physical source lines to form \defnx{logical source lines}{source line!logical}. Only the last
-backslash on any physical source line shall be eligible for being part
+backslash on any physical source line is eligible for being part
 of such a splice.
 \begin{note}
 Line splicing can form
 a \grammarterm{universal-character-name}\iref{lex.charset}.
 \end{note}
 A source file that is not empty and that (after splicing)
 does not end in a new-line character
-shall be processed as if an additional new-line character were appended
+is processed as if an additional new-line character were appended
 to the file.
 
 \item The source file is decomposed into preprocessing
@@ -415,7 +415,7 @@
 No other element of the translation character set
 is encoded with a code unit of value \tcode{0}.
 The code unit value of each decimal digit character after the digit \tcode{0} (\ucode{0030})
-shall be one greater than the value of the previous.
+is one greater than the value of the previous.
 The ordinary and wide literal encodings are otherwise
 \impldef{ordinary and wide literal encodings}.
 \indextext{UTF-8}%
@@ -609,7 +609,7 @@
 token shall be a raw string literal. Between the initial and final
 double quote characters of the raw string, any transformations performed in phase
 2 (line splicing) are reverted; this reversion
-shall apply before any \grammarterm{d-char}, \grammarterm{r-char}, or delimiting
+is applied before any \grammarterm{d-char}, \grammarterm{r-char}, or delimiting
 parenthesis is identified. The raw string literal is defined as the shortest sequence
 of characters that matches the raw-string pattern
 \begin{ncbnf}